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 $62.26   12.755%   $70.2013   $70.20   $70.20   $70.20  
  Purchase #2 $184.68   12.579%   $207.9109   $207.91   $207.90   $207.90  
  Purchase #3 $65.40   8.572%   $71.0061   $71.01   $71.00   $71.00  
  Purchase #4 $20.72   4.788%   $21.7121   $21.71   $21.70   $21.70  
  Purchase #5 $247.43   13.213%   $280.1229   $280.12   $280.10   $280.10  
  Purchase #6 $182.88   11.435%   $203.7923   $203.79   $203.80   $203.80  
  Purchase #7 $154.46   3.538%   $159.9248   $159.92   $159.90   $159.90  
  7 purchase totals = $917.83       $1,014.6704   $1,014.66   $1,014.60   $1,014.60