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 $67.28   11.801%   $75.2197   $75.22   $75.20   $75.20  
  Purchase #2 $135.90   7.321%   $145.8492   $145.85   $145.85   $145.80  
  Purchase #3 $213.80   3.446%   $221.1675   $221.17   $221.15   $221.20  
  Purchase #4 $121.93   7.229%   $130.7443   $130.74   $130.75   $130.70  
  Purchase #5 $122.73   4.497%   $128.2492   $128.25   $128.25   $128.20  
  Purchase #6 $163.30   5.772%   $172.7257   $172.73   $172.75   $172.70  
  Purchase #7 $121.66   5.497%   $128.3477   $128.35   $128.35   $128.30  
  7 purchase totals = $946.60       $1,002.3033   $1,002.31   $1,002.30   $1,002.10