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 $83.48   13.145%   $94.4534   $94.45   $94.45   $94.50  
  Purchase #2 $233.25   5.766%   $246.6992   $246.70   $246.70   $246.70  
  Purchase #3 $108.33   3.431%   $112.0468   $112.05   $112.05   $112.00  
  Purchase #4 $138.41   9.353%   $151.3555   $151.36   $151.35   $151.40  
  Purchase #5 $151.37   12.244%   $169.9037   $169.90   $169.90   $169.90  
  Purchase #6 $202.26   13.505%   $229.5752   $229.58   $229.60   $229.60  
  Purchase #7 $19.37   13.651%   $22.0142   $22.01   $22.00   $22.00  
  7 purchase totals = $936.47       $1,026.0480   $1,026.05   $1,026.05   $1,026.10