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 $227.66   6.190%   $241.7522   $241.75   $241.75   $241.80  
  Purchase #2 $163.25   6.723%   $174.2253   $174.23   $174.25   $174.20  
  Purchase #3 $57.95   11.810%   $64.7939   $64.79   $64.80   $64.80  
  Purchase #4 $120.47   10.753%   $133.4241   $133.42   $133.40   $133.40  
  Purchase #5 $165.64   5.850%   $175.3299   $175.33   $175.35   $175.30  
  Purchase #6 $196.41   13.706%   $223.33   $223.33   $223.35   $223.30  
  Purchase #7 $84.69   13.240%   $95.903   $95.90   $95.90   $95.90  
  7 purchase totals = $1,016.07       $1,108.7584   $1,108.75   $1,108.80   $1,108.70