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 $205.53   8.324%   $222.6383   $222.64   $222.65   $222.60  
  Purchase #2 $176.31   3.271%   $182.0771   $182.08   $182.10   $182.10  
  Purchase #3 $24.95   10.533%   $27.578   $27.58   $27.60   $27.60  
  Purchase #4 $194.86   4.324%   $203.2857   $203.29   $203.30   $203.30  
  Purchase #5 $136.77   13.598%   $155.368   $155.37   $155.35   $155.40  
  Purchase #6 $156.38   12.421%   $175.804   $175.80   $175.80   $175.80  
  Purchase #7 $126.31   5.155%   $132.8213   $132.82   $132.80   $132.80  
  7 purchase totals = $1,021.11       $1,099.5724   $1,099.58   $1,099.60   $1,099.60