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 $66.99   12.354%   $75.2659   $75.27   $75.25   $75.30  
  Purchase #2 $55.66   7.265%   $59.7037   $59.70   $59.70   $59.70  
  Purchase #3 $235.34   5.709%   $248.7756   $248.78   $248.80   $248.80  
  Purchase #4 $106.30   3.867%   $110.4106   $110.41   $110.40   $110.40  
  Purchase #5 $200.40   6.113%   $212.6505   $212.65   $212.65   $212.70  
  Purchase #6 $186.94   10.433%   $206.4435   $206.44   $206.45   $206.40  
  Purchase #7 $230.43   10.627%   $254.9178   $254.92   $254.90   $254.90  
  7 purchase totals = $1,082.06       $1,168.1676   $1,168.17   $1,168.15   $1,168.20