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 $194.98   12.844%   $220.0232   $220.02   $220.00   $220.00  
  Purchase #2 $95.53   10.467%   $105.5291   $105.53   $105.55   $105.50  
  Purchase #3 $153.65   10.586%   $169.9154   $169.92   $169.90   $169.90  
  Purchase #4 $225.63   6.197%   $239.6123   $239.61   $239.60   $239.60  
  Purchase #5 $131.53   11.849%   $147.115   $147.12   $147.10   $147.10  
  Purchase #6 $232.50   9.720%   $255.099   $255.10   $255.10   $255.10  
  Purchase #7 $231.62   11.168%   $257.4873   $257.49   $257.50   $257.50  
  7 purchase totals = $1,265.44       $1,394.7813   $1,394.79   $1,394.75   $1,394.70