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 $241.92   4.296%   $252.3129   $252.31   $252.30   $252.30  
  Purchase #2 $34.47   4.503%   $36.0222   $36.02   $36.00   $36.00  
  Purchase #3 $93.29   13.379%   $105.7713   $105.77   $105.75   $105.80  
  Purchase #4 $86.56   8.693%   $94.0847   $94.08   $94.10   $94.10  
  Purchase #5 $212.60   11.144%   $236.2921   $236.29   $236.30   $236.30  
  Purchase #6 $97.70   3.424%   $101.0452   $101.05   $101.05   $101.00  
  Purchase #7 $62.49   9.295%   $68.2984   $68.30   $68.30   $68.30  
  7 purchase totals = $829.03       $893.8268   $893.82   $893.80   $893.80