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 $180.56   8.588%   $196.0665   $196.07   $196.05   $196.10  
  Purchase #2 $50.81   6.686%   $54.2072   $54.21   $54.20   $54.20  
  Purchase #3 $24.96   9.312%   $27.2843   $27.28   $27.30   $27.30  
  Purchase #4 $199.34   6.420%   $212.1376   $212.14   $212.15   $212.10  
  Purchase #5 $250.67   6.532%   $267.0438   $267.04   $267.05   $267.00  
  Purchase #6 $84.55   13.152%   $95.67   $95.67   $95.65   $95.70  
  Purchase #7 $182.56   8.562%   $198.1908   $198.19   $198.20   $198.20  
  7 purchase totals = $973.45       $1,050.6002   $1,050.60   $1,050.60   $1,050.60