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 $164.33   7.124%   $176.0369   $176.04   $176.05   $176.00  
  Purchase #2 $146.79   13.362%   $166.4041   $166.40   $166.40   $166.40  
  Purchase #3 $117.49   9.795%   $128.9981   $129.00   $129.00   $129.00  
  Purchase #4 $65.49   8.347%   $70.9565   $70.96   $70.95   $71.00  
  Purchase #5 $232.85   3.687%   $241.4352   $241.44   $241.45   $241.40  
  Purchase #6 $124.57   4.664%   $130.3799   $130.38   $130.40   $130.40  
  Purchase #7 $141.42   3.300%   $146.0869   $146.09   $146.10   $146.10  
  7 purchase totals = $992.94       $1,060.2976   $1,060.31   $1,060.35   $1,060.30