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 $158.47   6.764%   $169.1889   $169.19   $169.20   $169.20  
  Purchase #2 $132.69   6.279%   $141.0216   $141.02   $141.00   $141.00  
  Purchase #3 $157.52   13.821%   $179.2908   $179.29   $179.30   $179.30  
  Purchase #4 $222.39   6.407%   $236.6385   $236.64   $236.65   $236.60  
  Purchase #5 $41.80   8.598%   $45.394   $45.39   $45.40   $45.40  
  Purchase #6 $124.88   9.201%   $136.3702   $136.37   $136.35   $136.40  
  Purchase #7 $178.64   13.143%   $202.1187   $202.12   $202.10   $202.10  
  7 purchase totals = $1,016.39       $1,110.0227   $1,110.02   $1,110.00   $1,110.00