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 $88.74   10.392%   $97.9619   $97.96   $97.95   $98.00  
  Purchase #2 $47.70   13.608%   $54.191   $54.19   $54.20   $54.20  
  Purchase #3 $211.67   12.507%   $238.1436   $238.14   $238.15   $238.10  
  Purchase #4 $207.91   11.414%   $231.6408   $231.64   $231.65   $231.60  
  Purchase #5 $68.35   12.471%   $76.8739   $76.87   $76.85   $76.90  
  Purchase #6 $193.76   4.357%   $202.2021   $202.20   $202.20   $202.20  
  Purchase #7 $112.43   9.809%   $123.4583   $123.46   $123.45   $123.50  
  7 purchase totals = $930.56       $1,024.4716   $1,024.46   $1,024.45   $1,024.50