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 $63.37   6.767%   $67.6582   $67.66   $67.65   $67.70  
  Purchase #2 $229.73   5.300%   $241.9057   $241.91   $241.90   $241.90  
  Purchase #3 $88.57   6.601%   $94.4165   $94.42   $94.40   $94.40  
  Purchase #4 $212.48   10.349%   $234.4696   $234.47   $234.45   $234.50  
  Purchase #5 $129.43   12.480%   $145.5829   $145.58   $145.60   $145.60  
  Purchase #6 $49.70   8.658%   $54.003   $54.00   $54.00   $54.00  
  Purchase #7 $92.40   4.499%   $96.5571   $96.56   $96.55   $96.60  
  7 purchase totals = $865.68       $934.5930   $934.60   $934.55   $934.70