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 $171.44   9.833%   $188.2977   $188.30   $188.30   $188.30  
  Purchase #2 $45.40   8.415%   $49.2204   $49.22   $49.20   $49.20  
  Purchase #3 $104.57   4.341%   $109.1094   $109.11   $109.10   $109.10  
  Purchase #4 $89.30   7.588%   $96.0761   $96.08   $96.10   $96.10  
  Purchase #5 $128.37   6.519%   $136.7384   $136.74   $136.75   $136.70  
  Purchase #6 $40.56   12.203%   $45.5095   $45.51   $45.50   $45.50  
  Purchase #7 $72.89   9.539%   $79.843   $79.84   $79.85   $79.80  
  7 purchase totals = $652.53       $704.7945   $704.80   $704.80   $704.70