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 $243.62   3.207%   $251.4329   $251.43   $251.45   $251.40  
  Purchase #2 $113.32   8.706%   $123.1856   $123.19   $123.20   $123.20  
  Purchase #3 $67.85   8.651%   $73.7197   $73.72   $73.70   $73.70  
  Purchase #4 $126.99   5.241%   $133.6455   $133.65   $133.65   $133.60  
  Purchase #5 $184.69   3.664%   $191.457   $191.46   $191.45   $191.50  
  Purchase #6 $205.47   8.701%   $223.3479   $223.35   $223.35   $223.30  
  Purchase #7 $47.72   9.191%   $52.1059   $52.11   $52.10   $52.10  
  7 purchase totals = $989.66       $1,048.8945   $1,048.91   $1,048.90   $1,048.80