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 $235.86   6.464%   $251.106   $251.11   $251.10   $251.10  
  Purchase #2 $187.81   13.223%   $212.6441   $212.64   $212.65   $212.60  
  Purchase #3 $85.78   4.448%   $89.5955   $89.60   $89.60   $89.60  
  Purchase #4 $126.88   6.369%   $134.961   $134.96   $134.95   $135.00  
  Purchase #5 $56.26   11.452%   $62.7029   $62.70   $62.70   $62.70  
  Purchase #6 $236.79   5.192%   $249.0841   $249.08   $249.10   $249.10  
  Purchase #7 $40.32   11.782%   $45.0705   $45.07   $45.05   $45.10  
  7 purchase totals = $969.70       $1,045.1641   $1,045.16   $1,045.15   $1,045.20