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 $197.86   8.164%   $214.0133   $214.01   $214.00   $214.00  
  Purchase #2 $31.73   12.633%   $35.7385   $35.74   $35.75   $35.70  
  Purchase #3 $58.98   13.363%   $66.8615   $66.86   $66.85   $66.90  
  Purchase #4 $69.98   8.204%   $75.7212   $75.72   $75.70   $75.70  
  Purchase #5 $142.31   10.377%   $157.0775   $157.08   $157.10   $157.10  
  Purchase #6 $107.83   7.448%   $115.8612   $115.86   $115.85   $115.90  
  Purchase #7 $167.36   12.723%   $188.6532   $188.65   $188.65   $188.70  
  7 purchase totals = $776.05       $853.9264   $853.92   $853.90   $854.00