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 $114.47   10.816%   $126.8511   $126.85   $126.85   $126.90  
  Purchase #2 $229.88   9.801%   $252.4105   $252.41   $252.40   $252.40  
  Purchase #3 $191.94   6.387%   $204.1992   $204.20   $204.20   $204.20  
  Purchase #4 $49.78   3.136%   $51.3411   $51.34   $51.35   $51.30  
  Purchase #5 $157.63   13.137%   $178.3379   $178.34   $178.35   $178.30  
  Purchase #6 $28.54   10.767%   $31.6129   $31.61   $31.60   $31.60  
  Purchase #7 $153.51   10.651%   $169.8604   $169.86   $169.85   $169.90  
  7 purchase totals = $925.75       $1,014.6131   $1,014.61   $1,014.60   $1,014.60