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 $181.28   8.180%   $196.1087   $196.11   $196.10   $196.10  
  Purchase #2 $246.69   8.335%   $267.2516   $267.25   $267.25   $267.30  
  Purchase #3 $245.52   12.863%   $277.1012   $277.10   $277.10   $277.10  
  Purchase #4 $47.25   7.610%   $50.8457   $50.85   $50.85   $50.80  
  Purchase #5 $245.95   4.357%   $256.666   $256.67   $256.65   $256.70  
  Purchase #6 $169.54   6.191%   $180.0362   $180.04   $180.05   $180.00  
  Purchase #7 $77.70   8.375%   $84.2074   $84.21   $84.20   $84.20  
  7 purchase totals = $1,213.93       $1,312.2168   $1,312.23   $1,312.20   $1,312.20