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 $173.61   3.115%   $179.018   $179.02   $179.00   $179.00  
  Purchase #2 $45.46   5.327%   $47.8817   $47.88   $47.90   $47.90  
  Purchase #3 $58.78   9.234%   $64.2077   $64.21   $64.20   $64.20  
  Purchase #4 $119.28   4.353%   $124.4723   $124.47   $124.45   $124.50  
  Purchase #5 $159.30   11.561%   $177.7167   $177.72   $177.70   $177.70  
  Purchase #6 $157.68   5.625%   $166.5495   $166.55   $166.55   $166.50  
  Purchase #7 $238.64   6.769%   $254.7935   $254.79   $254.80   $254.80  
  7 purchase totals = $952.75       $1,014.6394   $1,014.64   $1,014.60   $1,014.60