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 $172.26   6.259%   $183.0418   $183.04   $183.05   $183.00  
  Purchase #2 $216.44   8.411%   $234.6448   $234.64   $234.65   $234.60  
  Purchase #3 $46.60   12.461%   $52.4068   $52.41   $52.40   $52.40  
  Purchase #4 $239.96   7.152%   $257.1219   $257.12   $257.10   $257.10  
  Purchase #5 $233.53   13.417%   $264.8627   $264.86   $264.85   $264.90  
  Purchase #6 $110.32   9.158%   $120.4231   $120.42   $120.40   $120.40  
  Purchase #7 $229.65   11.736%   $256.6017   $256.60   $256.60   $256.60  
  7 purchase totals = $1,248.76       $1,369.1028   $1,369.09   $1,369.05   $1,369.00