Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.49   8.398%   $225.999   $226.00   $226.00   $226.00  
  Purchase #2 $120.90   7.165%   $129.5625   $129.56   $129.55   $129.60  
  Purchase #3 $206.60   3.518%   $213.8682   $213.87   $213.85   $213.90  
  Purchase #4 $157.75   10.838%   $174.8469   $174.85   $174.85   $174.80  
  Purchase #5 $137.40   5.572%   $145.0559   $145.06   $145.05   $145.10  
  Purchase #6 $169.54   11.786%   $189.522   $189.52   $189.50   $189.50  
  Purchase #7 $233.86   5.542%   $246.8205   $246.82   $246.80   $246.80  
  7 purchase totals = $1,234.54       $1,325.6750   $1,325.68   $1,325.60   $1,325.70