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 $63.67   5.162%   $66.9566   $66.96   $66.95   $67.00  
  Purchase #2 $176.26   10.839%   $195.3648   $195.36   $195.35   $195.40  
  Purchase #3 $201.35   12.518%   $226.555   $226.56   $226.55   $226.60  
  Purchase #4 $150.38   10.322%   $165.9022   $165.90   $165.90   $165.90  
  Purchase #5 $13.72   9.491%   $15.0222   $15.02   $15.00   $15.00  
  Purchase #6 $91.31   10.794%   $101.166   $101.17   $101.15   $101.20  
  Purchase #7 $228.97   11.502%   $255.3061   $255.31   $255.30   $255.30  
  7 purchase totals = $925.66       $1,026.2729   $1,026.28   $1,026.20   $1,026.40