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 $69.76   9.872%   $76.6467   $76.65   $76.65   $76.60  
  Purchase #2 $8.76   8.264%   $9.4839   $9.48   $9.50   $9.50  
  Purchase #3 $202.37   10.599%   $223.8192   $223.82   $223.80   $223.80  
  Purchase #4 $240.27   6.578%   $256.075   $256.08   $256.10   $256.10  
  Purchase #5 $41.31   13.228%   $46.7745   $46.77   $46.75   $46.80  
  Purchase #6 $147.82   8.468%   $160.3374   $160.34   $160.35   $160.30  
  Purchase #7 $239.97   13.206%   $271.6604   $271.66   $271.65   $271.70  
  7 purchase totals = $950.26       $1,044.7971   $1,044.80   $1,044.80   $1,044.80