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 $169.71   9.534%   $185.8902   $185.89   $185.90   $185.90  
  Purchase #2 $190.85   7.308%   $204.7973   $204.80   $204.80   $204.80  
  Purchase #3 $124.48   7.790%   $134.177   $134.18   $134.20   $134.20  
  Purchase #4 $21.77   11.565%   $24.2877   $24.29   $24.30   $24.30  
  Purchase #5 $206.79   12.825%   $233.3108   $233.31   $233.30   $233.30  
  Purchase #6 $146.40   6.691%   $156.1956   $156.20   $156.20   $156.20  
  Purchase #7 $89.54   7.590%   $96.3361   $96.34   $96.35   $96.30  
  7 purchase totals = $949.54       $1,034.9947   $1,035.01   $1,035.05   $1,035.00