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 $46.55   5.508%   $49.114   $49.11   $49.10   $49.10  
  Purchase #2 $243.35   9.582%   $266.6678   $266.67   $266.65   $266.70  
  Purchase #3 $48.49   6.638%   $51.7088   $51.71   $51.70   $51.70  
  Purchase #4 $225.60   12.494%   $253.7865   $253.79   $253.80   $253.80  
  Purchase #5 $16.48   5.311%   $17.3553   $17.36   $17.35   $17.40  
  Purchase #6 $200.59   9.534%   $219.7143   $219.71   $219.70   $219.70  
  Purchase #7 $48.29   4.757%   $50.5872   $50.59   $50.60   $50.60  
  7 purchase totals = $829.35       $908.9339   $908.94   $908.90   $909.00