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 $61.61   10.580%   $68.1283   $68.13   $68.15   $68.10  
  Purchase #2 $31.88   5.584%   $33.6602   $33.66   $33.65   $33.70  
  Purchase #3 $191.48   3.304%   $197.8065   $197.81   $197.80   $197.80  
  Purchase #4 $9.79   3.378%   $10.1207   $10.12   $10.10   $10.10  
  Purchase #5 $90.71   6.803%   $96.881   $96.88   $96.90   $96.90  
  Purchase #6 $166.95   3.142%   $172.1956   $172.20   $172.20   $172.20  
  Purchase #7 $223.66   10.395%   $246.9095   $246.91   $246.90   $246.90  
  7 purchase totals = $776.08       $825.7018   $825.71   $825.70   $825.70