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 $179.51   8.627%   $194.9963   $195.00   $195.00   $195.00  
  Purchase #2 $192.83   13.551%   $218.9604   $218.96   $218.95   $219.00  
  Purchase #3 $6.45   12.462%   $7.2538   $7.25   $7.25   $7.30  
  Purchase #4 $67.27   3.516%   $69.6352   $69.64   $69.65   $69.60  
  Purchase #5 $231.33   4.620%   $242.0174   $242.02   $242.00   $242.00  
  Purchase #6 $207.79   10.399%   $229.3981   $229.40   $229.40   $229.40  
  Purchase #7 $104.47   3.263%   $107.8789   $107.88   $107.90   $107.90  
  7 purchase totals = $989.65       $1,070.1401   $1,070.15   $1,070.15   $1,070.20