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 $85.57   6.184%   $90.8616   $90.86   $90.85   $90.90  
  Purchase #2 $25.60   5.288%   $26.9537   $26.95   $26.95   $27.00  
  Purchase #3 $110.67   5.538%   $116.7989   $116.80   $116.80   $116.80  
  Purchase #4 $124.41   9.156%   $135.801   $135.80   $135.80   $135.80  
  Purchase #5 $222.53   5.166%   $234.0259   $234.03   $234.05   $234.00  
  Purchase #6 $65.67   6.790%   $70.129   $70.13   $70.15   $70.10  
  Purchase #7 $102.72   8.601%   $111.5549   $111.55   $111.55   $111.60  
  7 purchase totals = $737.17       $786.1250   $786.12   $786.15   $786.20