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 $195.66   3.152%   $201.8272   $201.83   $201.85   $201.80  
  Purchase #2 $191.47   8.397%   $207.5477   $207.55   $207.55   $207.50  
  Purchase #3 $43.63   3.564%   $45.185   $45.19   $45.20   $45.20  
  Purchase #4 $99.31   10.496%   $109.7336   $109.73   $109.75   $109.70  
  Purchase #5 $60.43   13.279%   $68.4545   $68.45   $68.45   $68.50  
  Purchase #6 $34.79   11.433%   $38.7675   $38.77   $38.75   $38.80  
  Purchase #7 $120.81   12.249%   $135.608   $135.61   $135.60   $135.60  
  7 purchase totals = $746.10       $807.1235   $807.13   $807.15   $807.10