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 $215.70   5.222%   $226.9639   $226.96   $226.95   $227.00  
  Purchase #2 $29.50   12.148%   $33.0837   $33.08   $33.10   $33.10  
  Purchase #3 $39.86   6.311%   $42.3756   $42.38   $42.40   $42.40  
  Purchase #4 $97.97   4.678%   $102.553   $102.55   $102.55   $102.60  
  Purchase #5 $93.32   4.805%   $97.804   $97.80   $97.80   $97.80  
  Purchase #6 $236.84   5.293%   $249.3759   $249.38   $249.40   $249.40  
  Purchase #7 $226.68   9.822%   $248.9445   $248.94   $248.95   $248.90  
  7 purchase totals = $939.87       $1,001.1006   $1,001.09   $1,001.15   $1,001.20