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 $195.80   3.152%   $201.9716   $201.97   $201.95   $202.00  
  Purchase #2 $91.63   5.414%   $96.5908   $96.59   $96.60   $96.60  
  Purchase #3 $9.63   9.737%   $10.5677   $10.57   $10.55   $10.60  
  Purchase #4 $65.55   4.257%   $68.3405   $68.34   $68.35   $68.30  
  Purchase #5 $203.95   8.373%   $221.0267   $221.03   $221.05   $221.00  
  Purchase #6 $161.91   10.140%   $178.3277   $178.33   $178.35   $178.30  
  Purchase #7 $136.58   9.443%   $149.4772   $149.48   $149.50   $149.50  
  7 purchase totals = $865.05       $926.3022   $926.31   $926.35   $926.30