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 $167.40   5.733%   $176.997   $177.00   $177.00   $177.00  
  Purchase #2 $55.48   8.151%   $60.0022   $60.00   $60.00   $60.00  
  Purchase #3 $83.39   11.118%   $92.6613   $92.66   $92.65   $92.70  
  Purchase #4 $170.98   4.832%   $179.2418   $179.24   $179.25   $179.20  
  Purchase #5 $160.83   9.452%   $176.0317   $176.03   $176.05   $176.00  
  Purchase #6 $110.88   12.234%   $124.4451   $124.45   $124.45   $124.40  
  Purchase #7 $223.45   13.703%   $254.0694   $254.07   $254.05   $254.10  
  7 purchase totals = $972.41       $1,063.4485   $1,063.45   $1,063.45   $1,063.40