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 $177.57   11.323%   $197.6763   $197.68   $197.70   $197.70  
  Purchase #2 $189.81   5.606%   $200.4507   $200.45   $200.45   $200.50  
  Purchase #3 $39.56   9.192%   $43.1964   $43.20   $43.20   $43.20  
  Purchase #4 $66.48   13.350%   $75.3551   $75.36   $75.35   $75.40  
  Purchase #5 $166.60   4.203%   $173.6022   $173.60   $173.60   $173.60  
  Purchase #6 $81.93   12.816%   $92.4301   $92.43   $92.45   $92.40  
  Purchase #7 $164.98   5.661%   $174.3195   $174.32   $174.30   $174.30  
  7 purchase totals = $886.93       $957.0303   $957.04   $957.05   $957.10