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 $17.38   9.337%   $19.0028   $19.00   $19.00   $19.00  
  Purchase #2 $144.55   13.830%   $164.5413   $164.54   $164.55   $164.50  
  Purchase #3 $181.84   4.774%   $190.521   $190.52   $190.50   $190.50  
  Purchase #4 $204.69   6.567%   $218.132   $218.13   $218.15   $218.10  
  Purchase #5 $66.66   12.507%   $74.9972   $75.00   $75.00   $75.00  
  Purchase #6 $83.93   5.841%   $88.8324   $88.83   $88.85   $88.80  
  Purchase #7 $63.37   3.657%   $65.6874   $65.69   $65.70   $65.70  
  7 purchase totals = $762.42       $821.7141   $821.71   $821.75   $821.60