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 $227.25   8.137%   $245.7413   $245.74   $245.75   $245.70  
  Purchase #2 $131.98   11.485%   $147.1379   $147.14   $147.15   $147.10  
  Purchase #3 $247.39   9.587%   $271.1073   $271.11   $271.10   $271.10  
  Purchase #4 $234.58   3.670%   $243.1891   $243.19   $243.20   $243.20  
  Purchase #5 $210.36   12.356%   $236.3521   $236.35   $236.35   $236.40  
  Purchase #6 $131.29   11.289%   $146.1113   $146.11   $146.10   $146.10  
  Purchase #7 $69.75   8.420%   $75.623   $75.62   $75.60   $75.60  
  7 purchase totals = $1,252.60       $1,365.2620   $1,365.26   $1,365.25   $1,365.20