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 $29.47   8.646%   $32.018   $32.02   $32.00   $32.00  
  Purchase #2 $52.91   7.802%   $57.038   $57.04   $57.05   $57.00  
  Purchase #3 $62.88   7.859%   $67.8217   $67.82   $67.80   $67.80  
  Purchase #4 $101.26   3.382%   $104.6846   $104.68   $104.70   $104.70  
  Purchase #5 $123.48   4.247%   $128.7242   $128.72   $128.70   $128.70  
  Purchase #6 $201.97   5.243%   $212.5593   $212.56   $212.55   $212.60  
  Purchase #7 $185.54   12.834%   $209.3522   $209.35   $209.35   $209.40  
  7 purchase totals = $757.51       $812.1980   $812.19   $812.15   $812.20