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 $218.95   10.122%   $241.1121   $241.11   $241.10   $241.10  
  Purchase #2 $205.34   10.432%   $226.7611   $226.76   $226.75   $226.80  
  Purchase #3 $210.51   7.352%   $225.9867   $225.99   $226.00   $226.00  
  Purchase #4 $36.52   12.560%   $41.1069   $41.11   $41.10   $41.10  
  Purchase #5 $62.27   8.786%   $67.741   $67.74   $67.75   $67.70  
  Purchase #6 $174.96   12.707%   $197.1922   $197.19   $197.20   $197.20  
  Purchase #7 $59.65   4.111%   $62.1022   $62.10   $62.10   $62.10  
  7 purchase totals = $968.20       $1,062.0022   $1,062.00   $1,062.00   $1,062.00