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 $184.68   12.600%   $207.9497   $207.95   $207.95   $207.90  
  Purchase #2 $64.83   11.485%   $72.2757   $72.28   $72.30   $72.30  
  Purchase #3 $72.50   12.641%   $81.6647   $81.66   $81.65   $81.70  
  Purchase #4 $200.91   11.633%   $224.2819   $224.28   $224.30   $224.30  
  Purchase #5 $189.62   9.574%   $207.7742   $207.77   $207.75   $207.80  
  Purchase #6 $210.75   4.780%   $220.8239   $220.82   $220.80   $220.80  
  Purchase #7 $68.44   3.801%   $71.0414   $71.04   $71.05   $71.00  
  7 purchase totals = $991.73       $1,085.8115   $1,085.80   $1,085.80   $1,085.80