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 $106.88   8.716%   $116.1957   $116.20   $116.20   $116.20  
  Purchase #2 $137.50   3.486%   $142.2933   $142.29   $142.30   $142.30  
  Purchase #3 $249.27   8.443%   $270.3159   $270.32   $270.30   $270.30  
  Purchase #4 $48.65   10.252%   $53.6376   $53.64   $53.65   $53.60  
  Purchase #5 $230.35   6.201%   $244.634   $244.63   $244.65   $244.60  
  Purchase #6 $60.69   6.114%   $64.4006   $64.40   $64.40   $64.40  
  Purchase #7 $136.80   10.868%   $151.6674   $151.67   $151.65   $151.70  
  7 purchase totals = $970.14       $1,043.1445   $1,043.15   $1,043.15   $1,043.10