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 $89.65   6.492%   $95.4701   $95.47   $95.45   $95.50  
  Purchase #2 $170.46   8.742%   $185.3616   $185.36   $185.35   $185.40  
  Purchase #3 $229.55   6.611%   $244.7256   $244.73   $244.75   $244.70  
  Purchase #4 $216.60   11.683%   $241.9054   $241.91   $241.90   $241.90  
  Purchase #5 $11.70   3.283%   $12.0841   $12.08   $12.10   $12.10  
  Purchase #6 $191.40   5.180%   $201.3145   $201.31   $201.30   $201.30  
  Purchase #7 $52.90   10.289%   $58.3429   $58.34   $58.35   $58.30  
  7 purchase totals = $962.26       $1,039.2042   $1,039.20   $1,039.20   $1,039.20