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 $240.82   4.496%   $251.6473   $251.65   $251.65   $251.60  
  Purchase #2 $162.38   13.819%   $184.8193   $184.82   $184.80   $184.80  
  Purchase #3 $42.27   9.196%   $46.1571   $46.16   $46.15   $46.20  
  Purchase #4 $48.33   4.155%   $50.3381   $50.34   $50.35   $50.30  
  Purchase #5 $220.35   8.558%   $239.2076   $239.21   $239.20   $239.20  
  Purchase #6 $227.93   12.376%   $256.1386   $256.14   $256.15   $256.10  
  Purchase #7 $27.96   13.206%   $31.6524   $31.65   $31.65   $31.70  
  7 purchase totals = $970.04       $1,059.9604   $1,059.97   $1,059.95   $1,059.90