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 $34.46   6.619%   $36.7409   $36.74   $36.75   $36.70  
  Purchase #2 $204.32   11.563%   $227.9455   $227.95   $227.95   $227.90  
  Purchase #3 $125.63   8.864%   $136.7658   $136.77   $136.75   $136.80  
  Purchase #4 $243.52   9.689%   $267.1147   $267.11   $267.10   $267.10  
  Purchase #5 $53.86   4.111%   $56.0742   $56.07   $56.05   $56.10  
  Purchase #6 $116.67   12.653%   $131.4323   $131.43   $131.45   $131.40  
  Purchase #7 $34.89   11.188%   $38.7935   $38.79   $38.80   $38.80  
  7 purchase totals = $813.35       $894.8669   $894.86   $894.85   $894.80