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 $198.38   3.202%   $204.7321   $204.73   $204.75   $204.70  
  Purchase #2 $237.97   10.794%   $263.6565   $263.66   $263.65   $263.70  
  Purchase #3 $60.88   13.358%   $69.0124   $69.01   $69.00   $69.00  
  Purchase #4 $220.33   3.861%   $228.8369   $228.84   $228.85   $228.80  
  Purchase #5 $250.74   10.647%   $277.4363   $277.44   $277.45   $277.40  
  Purchase #6 $155.32   4.140%   $161.7502   $161.75   $161.75   $161.80  
  Purchase #7 $124.57   10.610%   $137.7869   $137.79   $137.80   $137.80  
  7 purchase totals = $1,248.19       $1,343.2113   $1,343.22   $1,343.25   $1,343.20