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 $83.86   12.714%   $94.522   $94.52   $94.50   $94.50  
  Purchase #2 $23.45   5.577%   $24.7578   $24.76   $24.75   $24.80  
  Purchase #3 $144.91   11.279%   $161.2544   $161.25   $161.25   $161.30  
  Purchase #4 $210.74   11.874%   $235.7633   $235.76   $235.75   $235.80  
  Purchase #5 $128.92   13.539%   $146.3745   $146.37   $146.35   $146.40  
  Purchase #6 $242.39   13.204%   $274.3952   $274.40   $274.40   $274.40  
  Purchase #7 $139.48   5.790%   $147.5559   $147.56   $147.55   $147.60  
  7 purchase totals = $973.75       $1,084.6231   $1,084.62   $1,084.55   $1,084.80