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 $57.47   13.138%   $65.0204   $65.02   $65.00   $65.00  
  Purchase #2 $203.43   13.478%   $230.8483   $230.85   $230.85   $230.80  
  Purchase #3 $177.65   9.572%   $194.6547   $194.65   $194.65   $194.70  
  Purchase #4 $221.84   5.554%   $234.161   $234.16   $234.15   $234.20  
  Purchase #5 $224.70   10.751%   $248.8575   $248.86   $248.85   $248.90  
  Purchase #6 $141.87   6.562%   $151.1795   $151.18   $151.20   $151.20  
  Purchase #7 $130.80   4.198%   $136.291   $136.29   $136.30   $136.30  
  7 purchase totals = $1,157.76       $1,261.0124   $1,261.01   $1,261.00   $1,261.10