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 $125.92   3.373%   $130.1673   $130.17   $130.15   $130.20  
  Purchase #2 $244.39   7.733%   $263.2887   $263.29   $263.30   $263.30  
  Purchase #3 $176.91   5.163%   $186.0439   $186.04   $186.05   $186.00  
  Purchase #4 $206.82   11.144%   $229.868   $229.87   $229.85   $229.90  
  Purchase #5 $101.50   8.307%   $109.9316   $109.93   $109.95   $109.90  
  Purchase #6 $79.90   3.220%   $82.4728   $82.47   $82.45   $82.50  
  Purchase #7 $60.61   6.557%   $64.5842   $64.58   $64.60   $64.60  
  7 purchase totals = $996.05       $1,066.3565   $1,066.35   $1,066.35   $1,066.40