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 $211.97   11.564%   $236.4822   $236.48   $236.50   $236.50  
  Purchase #2 $55.37   9.673%   $60.7259   $60.73   $60.75   $60.70  
  Purchase #3 $145.27   5.117%   $152.7035   $152.70   $152.70   $152.70  
  Purchase #4 $62.87   12.289%   $70.5961   $70.60   $70.60   $70.60  
  Purchase #5 $186.90   9.846%   $205.3022   $205.30   $205.30   $205.30  
  Purchase #6 $77.74   3.113%   $80.16   $80.16   $80.15   $80.20  
  Purchase #7 $85.58   3.720%   $88.7636   $88.76   $88.75   $88.80  
  7 purchase totals = $825.70       $894.7335   $894.73   $894.75   $894.80