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 $86.86   7.836%   $93.6663   $93.67   $93.65   $93.70  
  Purchase #2 $114.49   3.700%   $118.7261   $118.73   $118.75   $118.70  
  Purchase #3 $236.81   11.395%   $263.7945   $263.79   $263.80   $263.80  
  Purchase #4 $128.48   5.433%   $135.4603   $135.46   $135.45   $135.50  
  Purchase #5 $55.68   8.110%   $60.1956   $60.20   $60.20   $60.20  
  Purchase #6 $43.57   3.809%   $45.2296   $45.23   $45.25   $45.20  
  Purchase #7 $180.82   11.391%   $201.4172   $201.42   $201.40   $201.40  
  7 purchase totals = $846.71       $918.4896   $918.50   $918.50   $918.50