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 $88.91   13.733%   $101.12   $101.12   $101.10   $101.10  
  Purchase #2 $23.63   6.780%   $25.2321   $25.23   $25.25   $25.20  
  Purchase #3 $156.84   10.182%   $172.8094   $172.81   $172.80   $172.80  
  Purchase #4 $65.60   5.118%   $68.9574   $68.96   $68.95   $69.00  
  Purchase #5 $71.55   11.501%   $79.779   $79.78   $79.80   $79.80  
  Purchase #6 $192.67   12.438%   $216.6343   $216.63   $216.65   $216.60  
  Purchase #7 $178.51   10.700%   $197.6106   $197.61   $197.60   $197.60  
  7 purchase totals = $777.71       $862.1428   $862.14   $862.15   $862.10