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 $84.82   4.596%   $88.7183   $88.72   $88.70   $88.70  
  Purchase #2 $236.65   7.526%   $254.4603   $254.46   $254.45   $254.50  
  Purchase #3 $195.28   12.370%   $219.4361   $219.44   $219.45   $219.40  
  Purchase #4 $165.62   10.474%   $182.967   $182.97   $182.95   $183.00  
  Purchase #5 $230.65   11.659%   $257.5415   $257.54   $257.55   $257.50  
  Purchase #6 $43.69   7.710%   $47.0585   $47.06   $47.05   $47.10  
  Purchase #7 $212.43   3.347%   $219.54   $219.54   $219.55   $219.50  
  7 purchase totals = $1,169.14       $1,269.7217   $1,269.73   $1,269.70   $1,269.70