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 $56.89   13.669%   $64.6663   $64.67   $64.65   $64.70  
  Purchase #2 $227.44   7.649%   $244.8369   $244.84   $244.85   $244.80  
  Purchase #3 $20.30   6.374%   $21.5939   $21.59   $21.60   $21.60  
  Purchase #4 $148.87   12.703%   $167.781   $167.78   $167.80   $167.80  
  Purchase #5 $164.73   3.420%   $170.3638   $170.36   $170.35   $170.40  
  Purchase #6 $116.64   9.604%   $127.8421   $127.84   $127.85   $127.80  
  Purchase #7 $241.42   4.147%   $251.4317   $251.43   $251.45   $251.40  
  7 purchase totals = $976.29       $1,048.5157   $1,048.51   $1,048.55   $1,048.50