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 $44.91   6.291%   $47.7353   $47.74   $47.75   $47.70  
  Purchase #2 $228.83   13.175%   $258.9784   $258.98   $259.00   $259.00  
  Purchase #3 $156.90   10.779%   $173.8123   $173.81   $173.80   $173.80  
  Purchase #4 $119.79   13.400%   $135.8419   $135.84   $135.85   $135.80  
  Purchase #5 $186.95   13.225%   $211.6741   $211.67   $211.65   $211.70  
  Purchase #6 $29.55   6.496%   $31.4696   $31.47   $31.45   $31.50  
  Purchase #7 $209.55   13.489%   $237.8162   $237.82   $237.80   $237.80  
  7 purchase totals = $976.48       $1,097.3278   $1,097.33   $1,097.30   $1,097.30