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 $55.92   10.106%   $61.5713   $61.57   $61.55   $61.60  
  Purchase #2 $191.84   5.641%   $202.6617   $202.66   $202.65   $202.70  
  Purchase #3 $189.67   7.220%   $203.3642   $203.36   $203.35   $203.40  
  Purchase #4 $121.33   9.520%   $132.8806   $132.88   $132.90   $132.90  
  Purchase #5 $131.98   4.451%   $137.8544   $137.85   $137.85   $137.90  
  Purchase #6 $49.53   5.611%   $52.3091   $52.31   $52.30   $52.30  
  Purchase #7 $121.78   3.299%   $125.7975   $125.80   $125.80   $125.80  
  7 purchase totals = $862.05       $916.4388   $916.43   $916.40   $916.60