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 $178.45   12.541%   $200.8294   $200.83   $200.85   $200.80  
  Purchase #2 $221.72   4.794%   $232.3493   $232.35   $232.35   $232.30  
  Purchase #3 $54.38   11.661%   $60.7213   $60.72   $60.70   $60.70  
  Purchase #4 $97.73   11.213%   $108.6885   $108.69   $108.70   $108.70  
  Purchase #5 $154.84   5.376%   $163.1642   $163.16   $163.15   $163.20  
  Purchase #6 $172.33   9.491%   $188.6858   $188.69   $188.70   $188.70  
  Purchase #7 $101.74   6.321%   $108.171   $108.17   $108.15   $108.20  
  7 purchase totals = $981.19       $1,062.6095   $1,062.61   $1,062.60   $1,062.60