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 $71.94   9.192%   $78.5527   $78.55   $78.55   $78.60  
  Purchase #2 $213.97   9.659%   $234.6374   $234.64   $234.65   $234.60  
  Purchase #3 $156.87   8.873%   $170.7891   $170.79   $170.80   $170.80  
  Purchase #4 $85.38   9.451%   $93.4493   $93.45   $93.45   $93.40  
  Purchase #5 $162.73   13.298%   $184.3698   $184.37   $184.35   $184.40  
  Purchase #6 $196.30   5.350%   $206.8021   $206.80   $206.80   $206.80  
  Purchase #7 $45.29   10.405%   $50.0024   $50.00   $50.00   $50.00  
  7 purchase totals = $932.48       $1,018.6028   $1,018.60   $1,018.60   $1,018.60