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 $119.83   6.585%   $127.7208   $127.72   $127.70   $127.70  
  Purchase #2 $158.89   8.143%   $171.8284   $171.83   $171.85   $171.80  
  Purchase #3 $74.48   7.664%   $80.1881   $80.19   $80.20   $80.20  
  Purchase #4 $75.63   7.557%   $81.3454   $81.35   $81.35   $81.30  
  Purchase #5 $191.57   5.120%   $201.3784   $201.38   $201.40   $201.40  
  Purchase #6 $238.76   11.454%   $266.1076   $266.11   $266.10   $266.10  
  Purchase #7 $79.93   5.800%   $84.5659   $84.57   $84.55   $84.60  
  7 purchase totals = $939.09       $1,013.1346   $1,013.15   $1,013.15   $1,013.10