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 $185.81   11.228%   $206.6727   $206.67   $206.65   $206.70  
  Purchase #2 $234.46   6.288%   $249.2028   $249.20   $249.20   $249.20  
  Purchase #3 $81.80   11.434%   $91.153   $91.15   $91.15   $91.20  
  Purchase #4 $131.78   3.305%   $136.1353   $136.14   $136.15   $136.10  
  Purchase #5 $219.66   9.483%   $240.4904   $240.49   $240.50   $240.50  
  Purchase #6 $220.46   10.598%   $243.8244   $243.82   $243.80   $243.80  
  Purchase #7 $169.36   13.400%   $192.0542   $192.05   $192.05   $192.10  
  7 purchase totals = $1,243.33       $1,359.5328   $1,359.52   $1,359.50   $1,359.60