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 $88.76   6.628%   $94.643   $94.64   $94.65   $94.60  
  Purchase #2 $98.43   13.492%   $111.7102   $111.71   $111.70   $111.70  
  Purchase #3 $24.51   11.750%   $27.3899   $27.39   $27.40   $27.40  
  Purchase #4 $44.59   8.221%   $48.2557   $48.26   $48.25   $48.30  
  Purchase #5 $198.57   12.727%   $223.842   $223.84   $223.85   $223.80  
  Purchase #6 $22.53   5.261%   $23.7153   $23.72   $23.70   $23.70  
  Purchase #7 $157.31   8.222%   $170.244   $170.24   $170.25   $170.20  
  7 purchase totals = $634.70       $699.8001   $699.80   $699.80   $699.70