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 $227.86   6.743%   $243.2246   $243.22   $243.20   $243.20  
  Purchase #2 $175.50   11.370%   $195.4544   $195.45   $195.45   $195.50  
  Purchase #3 $183.35   8.148%   $198.2894   $198.29   $198.30   $198.30  
  Purchase #4 $87.43   12.204%   $98.1   $98.10   $98.10   $98.10  
  Purchase #5 $168.92   3.481%   $174.8001   $174.80   $174.80   $174.80  
  Purchase #6 $40.74   6.199%   $43.2655   $43.27   $43.25   $43.30  
  Purchase #7 $126.87   6.775%   $135.4654   $135.47   $135.45   $135.50  
  7 purchase totals = $1,010.67       $1,088.5994   $1,088.60   $1,088.55   $1,088.70