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 $91.87   4.494%   $95.9986   $96.00   $96.00   $96.00  
  Purchase #2 $14.78   12.129%   $16.5727   $16.57   $16.55   $16.60  
  Purchase #3 $194.57   9.401%   $212.8615   $212.86   $212.85   $212.90  
  Purchase #4 $186.55   8.577%   $202.5504   $202.55   $202.55   $202.60  
  Purchase #5 $116.34   6.225%   $123.5822   $123.58   $123.60   $123.60  
  Purchase #6 $173.29   6.148%   $183.9439   $183.94   $183.95   $183.90  
  Purchase #7 $204.58   5.697%   $216.2349   $216.23   $216.25   $216.20  
  7 purchase totals = $981.98       $1,051.7442   $1,051.73   $1,051.75   $1,051.80