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 $205.50   13.124%   $232.4698   $232.47   $232.45   $232.50  
  Purchase #2 $246.87   3.192%   $254.7501   $254.75   $254.75   $254.80  
  Purchase #3 $147.93   9.234%   $161.5899   $161.59   $161.60   $161.60  
  Purchase #4 $196.31   8.502%   $213.0003   $213.00   $213.00   $213.00  
  Purchase #5 $160.75   4.426%   $167.8648   $167.86   $167.85   $167.90  
  Purchase #6 $85.28   13.852%   $97.093   $97.09   $97.10   $97.10  
  Purchase #7 $60.29   7.799%   $64.992   $64.99   $65.00   $65.00  
  7 purchase totals = $1,102.93       $1,191.7599   $1,191.75   $1,191.75   $1,191.90