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 $63.73   12.580%   $71.7472   $71.75   $71.75   $71.70  
  Purchase #2 $95.39   12.517%   $107.33   $107.33   $107.35   $107.30  
  Purchase #3 $14.68   5.439%   $15.4784   $15.48   $15.50   $15.50  
  Purchase #4 $172.49   4.144%   $179.638   $179.64   $179.65   $179.60  
  Purchase #5 $111.38   9.150%   $121.5713   $121.57   $121.55   $121.60  
  Purchase #6 $197.61   7.334%   $212.1027   $212.10   $212.10   $212.10  
  Purchase #7 $52.35   13.592%   $59.4654   $59.47   $59.45   $59.50  
  7 purchase totals = $707.63       $767.3330   $767.34   $767.35   $767.30