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 $198.76   13.368%   $225.3302   $225.33   $225.35   $225.30  
  Purchase #2 $246.58   9.464%   $269.9163   $269.92   $269.90   $269.90  
  Purchase #3 $22.67   7.603%   $24.3936   $24.39   $24.40   $24.40  
  Purchase #4 $228.56   8.285%   $247.4962   $247.50   $247.50   $247.50  
  Purchase #5 $241.78   11.778%   $270.2568   $270.26   $270.25   $270.30  
  Purchase #6 $191.44   11.196%   $212.8736   $212.87   $212.85   $212.90  
  Purchase #7 $205.65   13.485%   $233.3819   $233.38   $233.40   $233.40  
  7 purchase totals = $1,335.44       $1,483.6486   $1,483.65   $1,483.65   $1,483.70