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 $118.64   6.827%   $126.7396   $126.74   $126.75   $126.70  
  Purchase #2 $142.48   9.376%   $155.8389   $155.84   $155.85   $155.80  
  Purchase #3 $116.47   8.707%   $126.611   $126.61   $126.60   $126.60  
  Purchase #4 $84.47   5.667%   $89.2569   $89.26   $89.25   $89.30  
  Purchase #5 $83.90   9.474%   $91.8487   $91.85   $91.85   $91.80  
  Purchase #6 $212.74   8.258%   $230.3081   $230.31   $230.30   $230.30  
  Purchase #7 $116.32   8.355%   $126.0385   $126.04   $126.05   $126.00  
  7 purchase totals = $875.02       $946.6417   $946.65   $946.65   $946.50