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 $11.41   11.803%   $12.7567   $12.76   $12.75   $12.80  
  Purchase #2 $44.58   13.755%   $50.712   $50.71   $50.70   $50.70  
  Purchase #3 $245.98   12.835%   $277.5515   $277.55   $277.55   $277.60  
  Purchase #4 $34.94   4.310%   $36.4459   $36.45   $36.45   $36.40  
  Purchase #5 $46.42   5.120%   $48.7967   $48.80   $48.80   $48.80  
  Purchase #6 $166.46   5.313%   $175.304   $175.30   $175.30   $175.30  
  Purchase #7 $147.51   5.502%   $155.626   $155.63   $155.65   $155.60  
  7 purchase totals = $697.30       $757.1928   $757.20   $757.20   $757.20