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 $218.43   11.341%   $243.2021   $243.20   $243.20   $243.20  
  Purchase #2 $120.67   12.522%   $135.7803   $135.78   $135.80   $135.80  
  Purchase #3 $55.82   11.857%   $62.4386   $62.44   $62.45   $62.40  
  Purchase #4 $52.58   5.771%   $55.6144   $55.61   $55.60   $55.60  
  Purchase #5 $184.61   4.374%   $192.6848   $192.68   $192.70   $192.70  
  Purchase #6 $64.84   12.313%   $72.8237   $72.82   $72.80   $72.80  
  Purchase #7 $26.92   11.184%   $29.9307   $29.93   $29.95   $29.90  
  7 purchase totals = $723.87       $792.4746   $792.46   $792.50   $792.40