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 $83.60   13.368%   $94.7756   $94.78   $94.80   $94.80  
  Purchase #2 $161.31   3.827%   $167.4833   $167.48   $167.50   $167.50  
  Purchase #3 $205.34   6.549%   $218.7877   $218.79   $218.80   $218.80  
  Purchase #4 $214.94   6.823%   $229.6054   $229.61   $229.60   $229.60  
  Purchase #5 $62.61   7.191%   $67.1123   $67.11   $67.10   $67.10  
  Purchase #6 $52.29   10.772%   $57.9227   $57.92   $57.90   $57.90  
  Purchase #7 $14.66   12.668%   $16.5171   $16.52   $16.50   $16.50  
  7 purchase totals = $794.75       $852.2041   $852.21   $852.20   $852.20