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 $88.45   6.490%   $94.1904   $94.19   $94.20   $94.20  
  Purchase #2 $36.94   6.454%   $39.3241   $39.32   $39.30   $39.30  
  Purchase #3 $84.34   6.156%   $89.532   $89.53   $89.55   $89.50  
  Purchase #4 $113.44   7.214%   $121.6236   $121.62   $121.60   $121.60  
  Purchase #5 $14.83   13.842%   $16.8828   $16.88   $16.90   $16.90  
  Purchase #6 $143.73   11.310%   $159.9859   $159.99   $160.00   $160.00  
  Purchase #7 $50.72   5.458%   $53.4883   $53.49   $53.50   $53.50  
  7 purchase totals = $532.45       $575.0271   $575.02   $575.05   $575.00