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 $80.54   9.261%   $87.9988   $88.00   $88.00   $88.00  
  Purchase #2 $94.84   8.242%   $102.6567   $102.66   $102.65   $102.70  
  Purchase #3 $90.89   5.747%   $96.1134   $96.11   $96.10   $96.10  
  Purchase #4 $205.91   13.586%   $233.8849   $233.88   $233.90   $233.90  
  Purchase #5 $59.74   3.543%   $61.8566   $61.86   $61.85   $61.90  
  Purchase #6 $194.54   6.541%   $207.2649   $207.26   $207.25   $207.30  
  Purchase #7 $59.57   10.832%   $66.0226   $66.02   $66.00   $66.00  
  7 purchase totals = $786.03       $855.7979   $855.79   $855.75   $855.90