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 $164.83   5.691%   $174.2105   $174.21   $174.20   $174.20  
  Purchase #2 $205.52   6.480%   $218.8377   $218.84   $218.85   $218.80  
  Purchase #3 $60.89   9.405%   $66.6167   $66.62   $66.60   $66.60  
  Purchase #4 $66.84   9.502%   $73.1911   $73.19   $73.20   $73.20  
  Purchase #5 $73.82   13.122%   $83.5067   $83.51   $83.50   $83.50  
  Purchase #6 $189.57   13.677%   $215.4975   $215.50   $215.50   $215.50  
  Purchase #7 $16.59   13.306%   $18.7975   $18.80   $18.80   $18.80  
  7 purchase totals = $778.06       $850.6577   $850.67   $850.65   $850.60