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 $227.43   3.117%   $234.519   $234.52   $234.50   $234.50  
  Purchase #2 $87.45   6.573%   $93.1981   $93.20   $93.20   $93.20  
  Purchase #3 $125.26   3.618%   $129.7919   $129.79   $129.80   $129.80  
  Purchase #4 $76.42   9.122%   $83.391   $83.39   $83.40   $83.40  
  Purchase #5 $7.84   9.437%   $8.5799   $8.58   $8.60   $8.60  
  Purchase #6 $184.40   4.449%   $192.604   $192.60   $192.60   $192.60  
  Purchase #7 $192.26   11.652%   $214.6621   $214.66   $214.65   $214.70  
  7 purchase totals = $901.06       $956.7460   $956.74   $956.75   $956.80