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 $82.65   5.308%   $87.0371   $87.04   $87.05   $87.00  
  Purchase #2 $93.40   11.437%   $104.0822   $104.08   $104.10   $104.10  
  Purchase #3 $44.75   5.865%   $47.3746   $47.37   $47.35   $47.40  
  Purchase #4 $153.89   7.617%   $165.6118   $165.61   $165.60   $165.60  
  Purchase #5 $243.80   7.662%   $262.48   $262.48   $262.50   $262.50  
  Purchase #6 $22.78   11.112%   $25.3113   $25.31   $25.30   $25.30  
  Purchase #7 $35.66   12.532%   $40.1289   $40.13   $40.15   $40.10  
  7 purchase totals = $676.93       $732.0259   $732.02   $732.05   $732.00