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 $173.83   7.711%   $187.234   $187.23   $187.25   $187.20  
  Purchase #2 $53.48   6.177%   $56.7835   $56.78   $56.80   $56.80  
  Purchase #3 $125.48   7.587%   $135.0002   $135.00   $135.00   $135.00  
  Purchase #4 $110.92   6.520%   $118.152   $118.15   $118.15   $118.20  
  Purchase #5 $166.86   8.702%   $181.3802   $181.38   $181.40   $181.40  
  Purchase #6 $95.91   12.118%   $107.5324   $107.53   $107.55   $107.50  
  Purchase #7 $60.85   6.753%   $64.9592   $64.96   $64.95   $65.00  
  7 purchase totals = $787.33       $851.0415   $851.03   $851.10   $851.10