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 $77.84   13.422%   $88.2877   $88.29   $88.30   $88.30  
  Purchase #2 $204.56   11.123%   $227.3132   $227.31   $227.30   $227.30  
  Purchase #3 $152.90   7.149%   $163.8308   $163.83   $163.85   $163.80  
  Purchase #4 $198.68   13.562%   $225.625   $225.63   $225.65   $225.60  
  Purchase #5 $235.57   3.360%   $243.4852   $243.49   $243.50   $243.50  
  Purchase #6 $161.97   6.167%   $171.9587   $171.96   $171.95   $172.00  
  Purchase #7 $213.82   9.792%   $234.7573   $234.76   $234.75   $234.80  
  7 purchase totals = $1,245.34       $1,355.2579   $1,355.27   $1,355.30   $1,355.30