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 $189.44   7.158%   $203.0001   $203.00   $203.00   $203.00  
  Purchase #2 $111.80   10.547%   $123.5915   $123.59   $123.60   $123.60  
  Purchase #3 $217.69   9.602%   $238.5926   $238.59   $238.60   $238.60  
  Purchase #4 $234.89   12.435%   $264.0986   $264.10   $264.10   $264.10  
  Purchase #5 $233.50   7.518%   $251.0545   $251.05   $251.05   $251.10  
  Purchase #6 $106.30   11.222%   $118.229   $118.23   $118.25   $118.20  
  Purchase #7 $238.71   7.667%   $257.0119   $257.01   $257.00   $257.00  
  7 purchase totals = $1,332.33       $1,455.5782   $1,455.57   $1,455.60   $1,455.60