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 $113.28   11.812%   $126.6606   $126.66   $126.65   $126.70  
  Purchase #2 $20.44   8.732%   $22.2248   $22.22   $22.20   $22.20  
  Purchase #3 $181.81   7.495%   $195.4367   $195.44   $195.45   $195.40  
  Purchase #4 $110.98   5.420%   $116.9951   $117.00   $117.00   $117.00  
  Purchase #5 $202.53   11.741%   $226.309   $226.31   $226.30   $226.30  
  Purchase #6 $192.87   10.129%   $212.4058   $212.41   $212.40   $212.40  
  Purchase #7 $58.64   12.592%   $66.0239   $66.02   $66.00   $66.00  
  7 purchase totals = $880.55       $966.0559   $966.06   $966.00   $966.00