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 $220.57   11.614%   $246.187   $246.19   $246.20   $246.20  
  Purchase #2 $31.35   9.440%   $34.3094   $34.31   $34.30   $34.30  
  Purchase #3 $227.46   7.670%   $244.9062   $244.91   $244.90   $244.90  
  Purchase #4 $170.60   5.869%   $180.6125   $180.61   $180.60   $180.60  
  Purchase #5 $220.69   3.240%   $227.8404   $227.84   $227.85   $227.80  
  Purchase #6 $209.25   6.665%   $223.1965   $223.20   $223.20   $223.20  
  Purchase #7 $201.64   9.263%   $220.3179   $220.32   $220.30   $220.30  
  7 purchase totals = $1,281.56       $1,377.3699   $1,377.38   $1,377.35   $1,377.30