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 $126.68   11.825%   $141.6599   $141.66   $141.65   $141.70  
  Purchase #2 $125.30   10.246%   $138.1382   $138.14   $138.15   $138.10  
  Purchase #3 $156.91   12.802%   $176.9976   $177.00   $177.00   $177.00  
  Purchase #4 $95.41   3.485%   $98.735   $98.74   $98.75   $98.70  
  Purchase #5 $179.97   11.674%   $200.9797   $200.98   $201.00   $201.00  
  Purchase #6 $224.44   3.492%   $232.2774   $232.28   $232.30   $232.30  
  Purchase #7 $62.46   4.754%   $65.4293   $65.43   $65.45   $65.40  
  7 purchase totals = $971.17       $1,054.2171   $1,054.23   $1,054.30   $1,054.20