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 $245.62   7.733%   $264.6138   $264.61   $264.60   $264.60  
  Purchase #2 $39.68   4.268%   $41.3735   $41.37   $41.35   $41.40  
  Purchase #3 $235.97   11.492%   $263.0877   $263.09   $263.10   $263.10  
  Purchase #4 $128.29   11.617%   $143.1934   $143.19   $143.20   $143.20  
  Purchase #5 $202.85   11.862%   $226.9121   $226.91   $226.90   $226.90  
  Purchase #6 $197.47   12.871%   $222.8864   $222.89   $222.90   $222.90  
  Purchase #7 $104.87   5.151%   $110.2719   $110.27   $110.25   $110.30  
  7 purchase totals = $1,154.75       $1,272.3388   $1,272.33   $1,272.30   $1,272.40