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 $175.56   4.227%   $182.9809   $182.98   $183.00   $183.00  
  Purchase #2 $85.32   9.145%   $93.1225   $93.12   $93.10   $93.10  
  Purchase #3 $90.87   5.868%   $96.2023   $96.20   $96.20   $96.20  
  Purchase #4 $145.53   8.144%   $157.382   $157.38   $157.40   $157.40  
  Purchase #5 $238.52   6.694%   $254.4865   $254.49   $254.50   $254.50  
  Purchase #6 $92.49   11.590%   $103.2096   $103.21   $103.20   $103.20  
  Purchase #7 $49.74   6.205%   $52.8264   $52.83   $52.85   $52.80  
  7 purchase totals = $878.03       $940.2102   $940.21   $940.25   $940.20