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 $238.39   11.588%   $266.0146   $266.01   $266.00   $266.00  
  Purchase #2 $57.94   11.827%   $64.7926   $64.79   $64.80   $64.80  
  Purchase #3 $105.72   4.739%   $110.7301   $110.73   $110.75   $110.70  
  Purchase #4 $125.41   8.683%   $136.2994   $136.30   $136.30   $136.30  
  Purchase #5 $81.39   11.722%   $90.9305   $90.93   $90.95   $90.90  
  Purchase #6 $170.64   3.617%   $176.812   $176.81   $176.80   $176.80  
  Purchase #7 $172.79   7.113%   $185.0806   $185.08   $185.10   $185.10  
  7 purchase totals = $952.28       $1,030.6598   $1,030.65   $1,030.70   $1,030.60