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 $245.90   10.868%   $272.6244   $272.62   $272.60   $272.60  
  Purchase #2 $194.75   11.133%   $216.4315   $216.43   $216.45   $216.40  
  Purchase #3 $61.96   12.625%   $69.7825   $69.78   $69.80   $69.80  
  Purchase #4 $181.34   3.285%   $187.297   $187.30   $187.30   $187.30  
  Purchase #5 $160.73   5.846%   $170.1263   $170.13   $170.15   $170.10  
  Purchase #6 $76.31   7.769%   $82.2385   $82.24   $82.25   $82.20  
  Purchase #7 $62.33   9.430%   $68.2077   $68.21   $68.20   $68.20  
  7 purchase totals = $983.32       $1,066.7079   $1,066.71   $1,066.75   $1,066.60