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 $24.81   10.158%   $27.3302   $27.33   $27.35   $27.30  
  Purchase #2 $162.55   8.345%   $176.1148   $176.11   $176.10   $176.10  
  Purchase #3 $185.67   9.530%   $203.3644   $203.36   $203.35   $203.40  
  Purchase #4 $220.93   10.196%   $243.456   $243.46   $243.45   $243.50  
  Purchase #5 $93.75   5.631%   $99.0291   $99.03   $99.05   $99.00  
  Purchase #6 $202.94   9.339%   $221.8926   $221.89   $221.90   $221.90  
  Purchase #7 $72.59   13.107%   $82.1044   $82.10   $82.10   $82.10  
  7 purchase totals = $963.24       $1,053.2915   $1,053.28   $1,053.30   $1,053.30