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 $239.90   6.604%   $255.743   $255.74   $255.75   $255.70  
  Purchase #2 $9.27   9.735%   $10.1724   $10.17   $10.15   $10.20  
  Purchase #3 $95.40   10.352%   $105.2758   $105.28   $105.30   $105.30  
  Purchase #4 $104.27   6.218%   $110.7535   $110.75   $110.75   $110.80  
  Purchase #5 $187.76   8.124%   $203.0136   $203.01   $203.00   $203.00  
  Purchase #6 $211.27   11.510%   $235.5872   $235.59   $235.60   $235.60  
  Purchase #7 $245.56   10.625%   $271.6508   $271.65   $271.65   $271.70  
  7 purchase totals = $1,093.43       $1,192.1963   $1,192.19   $1,192.20   $1,192.30