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 $174.61   12.727%   $196.8326   $196.83   $196.85   $196.80  
  Purchase #2 $98.99   7.759%   $106.6706   $106.67   $106.65   $106.70  
  Purchase #3 $102.32   11.111%   $113.6888   $113.69   $113.70   $113.70  
  Purchase #4 $59.68   7.519%   $64.1673   $64.17   $64.15   $64.20  
  Purchase #5 $199.88   3.397%   $206.6699   $206.67   $206.65   $206.70  
  Purchase #6 $11.56   9.465%   $12.6542   $12.65   $12.65   $12.70  
  Purchase #7 $230.43   10.274%   $254.1044   $254.10   $254.10   $254.10  
  7 purchase totals = $877.47       $954.7878   $954.78   $954.75   $954.90