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 $207.61   3.475%   $214.8244   $214.82   $214.80   $214.80  
  Purchase #2 $54.43   7.744%   $58.6451   $58.65   $58.65   $58.60  
  Purchase #3 $232.95   7.194%   $249.7084   $249.71   $249.70   $249.70  
  Purchase #4 $16.66   8.294%   $18.0418   $18.04   $18.05   $18.00  
  Purchase #5 $186.31   9.760%   $204.4939   $204.49   $204.50   $204.50  
  Purchase #6 $234.95   4.256%   $244.9495   $244.95   $244.95   $244.90  
  Purchase #7 $45.72   12.220%   $51.307   $51.31   $51.30   $51.30  
  7 purchase totals = $978.63       $1,041.9701   $1,041.97   $1,041.95   $1,041.80