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 $65.56   11.700%   $73.2305   $73.23   $73.25   $73.20  
  Purchase #2 $132.25   12.129%   $148.2906   $148.29   $148.30   $148.30  
  Purchase #3 $237.68   7.221%   $254.8429   $254.84   $254.85   $254.80  
  Purchase #4 $180.93   8.832%   $196.9097   $196.91   $196.90   $196.90  
  Purchase #5 $213.95   7.744%   $230.5183   $230.52   $230.50   $230.50  
  Purchase #6 $203.80   10.487%   $225.1725   $225.17   $225.15   $225.20  
  Purchase #7 $52.56   10.146%   $57.8927   $57.89   $57.90   $57.90  
  7 purchase totals = $1,086.73       $1,186.8572   $1,186.85   $1,186.85   $1,186.80