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 $131.67   5.215%   $138.5366   $138.54   $138.55   $138.50  
  Purchase #2 $201.69   12.441%   $226.7823   $226.78   $226.80   $226.80  
  Purchase #3 $59.61   4.707%   $62.4158   $62.42   $62.40   $62.40  
  Purchase #4 $209.52   10.751%   $232.0455   $232.05   $232.05   $232.00  
  Purchase #5 $59.88   5.138%   $62.9566   $62.96   $62.95   $63.00  
  Purchase #6 $237.37   4.187%   $247.3087   $247.31   $247.30   $247.30  
  Purchase #7 $56.66   9.451%   $62.0149   $62.01   $62.00   $62.00  
  7 purchase totals = $956.40       $1,032.0604   $1,032.07   $1,032.05   $1,032.00