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 $236.52   11.782%   $264.3868   $264.39   $264.40   $264.40  
  Purchase #2 $72.82   3.264%   $75.1968   $75.20   $75.20   $75.20  
  Purchase #3 $117.48   10.107%   $129.3537   $129.35   $129.35   $129.40  
  Purchase #4 $209.26   10.650%   $231.5462   $231.55   $231.55   $231.50  
  Purchase #5 $61.26   10.624%   $67.7683   $67.77   $67.75   $67.80  
  Purchase #6 $163.71   9.106%   $178.6174   $178.62   $178.60   $178.60  
  Purchase #7 $137.29   8.861%   $149.4553   $149.46   $149.45   $149.50  
  7 purchase totals = $998.34       $1,096.3245   $1,096.34   $1,096.30   $1,096.40