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 $237.87   12.530%   $267.6751   $267.68   $267.70   $267.70  
  Purchase #2 $50.64   7.341%   $54.3575   $54.36   $54.35   $54.40  
  Purchase #3 $217.62   12.444%   $244.7006   $244.70   $244.70   $244.70  
  Purchase #4 $241.86   11.654%   $270.0464   $270.05   $270.05   $270.00  
  Purchase #5 $59.39   5.508%   $62.6612   $62.66   $62.65   $62.70  
  Purchase #6 $241.89   4.556%   $252.9105   $252.91   $252.90   $252.90  
  Purchase #7 $19.62   11.313%   $21.8396   $21.84   $21.85   $21.80  
  7 purchase totals = $1,068.89       $1,174.1909   $1,174.20   $1,174.20   $1,174.20