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 $244.79   11.114%   $271.996   $272.00   $272.00   $272.00  
  Purchase #2 $213.56   6.702%   $227.8728   $227.87   $227.85   $227.90  
  Purchase #3 $221.51   7.404%   $237.9106   $237.91   $237.90   $237.90  
  Purchase #4 $117.73   11.525%   $131.2984   $131.30   $131.30   $131.30  
  Purchase #5 $37.44   9.112%   $40.8515   $40.85   $40.85   $40.90  
  Purchase #6 $42.98   12.510%   $48.3568   $48.36   $48.35   $48.40  
  Purchase #7 $216.53   12.478%   $243.5486   $243.55   $243.55   $243.50  
  7 purchase totals = $1,094.54       $1,201.8347   $1,201.84   $1,201.80   $1,201.90