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 $74.56   13.760%   $84.8195   $84.82   $84.80   $84.80  
  Purchase #2 $202.87   13.347%   $229.9471   $229.95   $229.95   $229.90  
  Purchase #3 $114.59   7.501%   $123.1854   $123.19   $123.20   $123.20  
  Purchase #4 $109.98   10.282%   $121.2881   $121.29   $121.30   $121.30  
  Purchase #5 $216.96   6.458%   $230.9713   $230.97   $230.95   $231.00  
  Purchase #6 $46.97   3.636%   $48.6778   $48.68   $48.70   $48.70  
  Purchase #7 $191.77   8.699%   $208.4521   $208.45   $208.45   $208.50  
  7 purchase totals = $957.70       $1,047.3413   $1,047.35   $1,047.35   $1,047.40