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 $117.49   11.547%   $131.0566   $131.06   $131.05   $131.10  
  Purchase #2 $200.51   9.594%   $219.7469   $219.75   $219.75   $219.70  
  Purchase #3 $60.56   9.379%   $66.2399   $66.24   $66.25   $66.20  
  Purchase #4 $92.77   6.146%   $98.4716   $98.47   $98.45   $98.50  
  Purchase #5 $83.36   6.677%   $88.9259   $88.93   $88.95   $88.90  
  Purchase #6 $169.97   6.409%   $180.8634   $180.86   $180.85   $180.90  
  Purchase #7 $232.95   5.867%   $246.6172   $246.62   $246.60   $246.60  
  7 purchase totals = $957.61       $1,031.9215   $1,031.93   $1,031.90   $1,031.90