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 $178.63   10.674%   $197.697   $197.70   $197.70   $197.70  
  Purchase #2 $165.60   9.256%   $180.9279   $180.93   $180.95   $180.90  
  Purchase #3 $230.54   3.616%   $238.8763   $238.88   $238.90   $238.90  
  Purchase #4 $16.75   10.691%   $18.5407   $18.54   $18.55   $18.50  
  Purchase #5 $205.97   13.245%   $233.2507   $233.25   $233.25   $233.30  
  Purchase #6 $63.73   11.480%   $71.0462   $71.05   $71.05   $71.00  
  Purchase #7 $13.59   6.785%   $14.5121   $14.51   $14.50   $14.50  
  7 purchase totals = $874.81       $954.8509   $954.86   $954.90   $954.80