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 $86.35   8.677%   $93.8426   $93.84   $93.85   $93.80  
  Purchase #2 $192.52   6.839%   $205.6864   $205.69   $205.70   $205.70  
  Purchase #3 $149.90   10.456%   $165.5735   $165.57   $165.55   $165.60  
  Purchase #4 $16.99   13.322%   $19.2534   $19.25   $19.25   $19.30  
  Purchase #5 $228.75   5.687%   $241.759   $241.76   $241.75   $241.80  
  Purchase #6 $231.40   10.754%   $256.2848   $256.28   $256.30   $256.30  
  Purchase #7 $225.78   6.579%   $240.6341   $240.63   $240.65   $240.60  
  7 purchase totals = $1,131.69       $1,223.0338   $1,223.02   $1,223.05   $1,223.10