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 $113.47   4.734%   $118.8417   $118.84   $118.85   $118.80  
  Purchase #2 $32.90   4.308%   $34.3173   $34.32   $34.30   $34.30  
  Purchase #3 $172.93   11.727%   $193.2095   $193.21   $193.20   $193.20  
  Purchase #4 $243.39   9.507%   $266.5291   $266.53   $266.55   $266.50  
  Purchase #5 $49.94   12.753%   $56.3088   $56.31   $56.30   $56.30  
  Purchase #6 $242.56   3.843%   $251.8816   $251.88   $251.90   $251.90  
  Purchase #7 $226.30   9.513%   $247.8279   $247.83   $247.85   $247.80  
  7 purchase totals = $1,081.49       $1,168.9159   $1,168.92   $1,168.95   $1,168.80