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 $55.81   12.561%   $62.8203   $62.82   $62.80   $62.80  
  Purchase #2 $41.69   7.753%   $44.9222   $44.92   $44.90   $44.90  
  Purchase #3 $139.60   9.483%   $152.8383   $152.84   $152.85   $152.80  
  Purchase #4 $120.72   10.416%   $133.2942   $133.29   $133.30   $133.30  
  Purchase #5 $230.95   6.508%   $245.9802   $245.98   $246.00   $246.00  
  Purchase #6 $48.55   8.621%   $52.7355   $52.74   $52.75   $52.70  
  Purchase #7 $31.59   3.127%   $32.5778   $32.58   $32.60   $32.60  
  7 purchase totals = $668.91       $725.1685   $725.17   $725.20   $725.10