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 $227.62   6.323%   $242.0124   $242.01   $242.00   $242.00  
  Purchase #2 $172.53   12.434%   $193.9824   $193.98   $194.00   $194.00  
  Purchase #3 $41.72   5.651%   $44.0776   $44.08   $44.10   $44.10  
  Purchase #4 $231.83   11.585%   $258.6875   $258.69   $258.70   $258.70  
  Purchase #5 $17.75   12.257%   $19.9256   $19.93   $19.95   $19.90  
  Purchase #6 $186.47   5.343%   $196.4331   $196.43   $196.45   $196.40  
  Purchase #7 $237.35   3.782%   $246.3266   $246.33   $246.35   $246.30  
  7 purchase totals = $1,115.27       $1,201.4452   $1,201.45   $1,201.55   $1,201.40