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 $85.42   3.665%   $88.5506   $88.55   $88.55   $88.60  
  Purchase #2 $186.84   8.634%   $202.9718   $202.97   $202.95   $203.00  
  Purchase #3 $13.28   6.245%   $14.1093   $14.11   $14.10   $14.10  
  Purchase #4 $154.82   6.319%   $164.6031   $164.60   $164.60   $164.60  
  Purchase #5 $181.91   13.181%   $205.8876   $205.89   $205.90   $205.90  
  Purchase #6 $129.67   3.472%   $134.1721   $134.17   $134.15   $134.20  
  Purchase #7 $234.63   5.684%   $247.9664   $247.97   $247.95   $248.00  
  7 purchase totals = $986.57       $1,058.2609   $1,058.26   $1,058.20   $1,058.40