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 $194.69   8.245%   $210.7422   $210.74   $210.75   $210.70  
  Purchase #2 $176.93   13.710%   $201.1871   $201.19   $201.20   $201.20  
  Purchase #3 $231.42   11.221%   $257.3876   $257.39   $257.40   $257.40  
  Purchase #4 $88.65   5.509%   $93.5337   $93.53   $93.55   $93.50  
  Purchase #5 $56.67   4.272%   $59.0909   $59.09   $59.10   $59.10  
  Purchase #6 $243.61   3.737%   $252.7137   $252.71   $252.70   $252.70  
  Purchase #7 $180.72   4.559%   $188.959   $188.96   $188.95   $189.00  
  7 purchase totals = $1,172.69       $1,263.6142   $1,263.61   $1,263.65   $1,263.60