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 $77.36   8.468%   $83.9108   $83.91   $83.90   $83.90  
  Purchase #2 $178.37   12.666%   $200.9623   $200.96   $200.95   $201.00  
  Purchase #3 $183.94   5.262%   $193.6189   $193.62   $193.60   $193.60  
  Purchase #4 $147.70   5.111%   $155.2489   $155.25   $155.25   $155.20  
  Purchase #5 $117.53   7.519%   $126.3671   $126.37   $126.35   $126.40  
  Purchase #6 $231.96   6.621%   $247.3181   $247.32   $247.30   $247.30  
  Purchase #7 $22.85   7.374%   $24.535   $24.54   $24.55   $24.50  
  7 purchase totals = $959.71       $1,031.9611   $1,031.97   $1,031.90   $1,031.90