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 $91.71   6.374%   $97.5556   $97.56   $97.55   $97.60  
  Purchase #2 $135.71   4.123%   $141.3053   $141.31   $141.30   $141.30  
  Purchase #3 $22.78   6.111%   $24.1721   $24.17   $24.15   $24.20  
  Purchase #4 $23.56   5.178%   $24.7799   $24.78   $24.80   $24.80  
  Purchase #5 $173.79   5.844%   $183.9463   $183.95   $183.95   $183.90  
  Purchase #6 $11.66   11.576%   $13.0098   $13.01   $13.00   $13.00  
  Purchase #7 $75.28   11.699%   $84.087   $84.09   $84.10   $84.10  
  7 purchase totals = $534.49       $568.8560   $568.87   $568.85   $568.90