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 $236.92   6.154%   $251.5001   $251.50   $251.50   $251.50  
  Purchase #2 $30.44   8.818%   $33.1242   $33.12   $33.10   $33.10  
  Purchase #3 $155.42   11.722%   $173.6383   $173.64   $173.65   $173.60  
  Purchase #4 $91.99   3.396%   $95.114   $95.11   $95.10   $95.10  
  Purchase #5 $184.25   7.122%   $197.3723   $197.37   $197.35   $197.40  
  Purchase #6 $124.52   6.157%   $132.1867   $132.19   $132.20   $132.20  
  Purchase #7 $118.99   4.207%   $123.9959   $124.00   $124.00   $124.00  
  7 purchase totals = $942.53       $1,006.9315   $1,006.93   $1,006.90   $1,006.90