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 $45.99   13.298%   $52.1058   $52.11   $52.10   $52.10  
  Purchase #2 $197.26   4.618%   $206.3695   $206.37   $206.35   $206.40  
  Purchase #3 $194.54   8.778%   $211.6167   $211.62   $211.60   $211.60  
  Purchase #4 $92.67   8.603%   $100.6424   $100.64   $100.65   $100.60  
  Purchase #5 $196.74   3.286%   $203.2049   $203.20   $203.20   $203.20  
  Purchase #6 $83.51   13.129%   $94.474   $94.47   $94.45   $94.50  
  Purchase #7 $230.72   9.662%   $253.0122   $253.01   $253.00   $253.00  
  7 purchase totals = $1,041.43       $1,121.4255   $1,121.42   $1,121.35   $1,121.40