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 $177.97   10.653%   $196.9291   $196.93   $196.95   $196.90  
  Purchase #2 $228.62   8.637%   $248.3659   $248.37   $248.35   $248.40  
  Purchase #3 $8.85   5.455%   $9.3328   $9.33   $9.35   $9.30  
  Purchase #4 $199.28   9.685%   $218.5803   $218.58   $218.60   $218.60  
  Purchase #5 $178.79   9.245%   $195.3191   $195.32   $195.30   $195.30  
  Purchase #6 $111.42   8.299%   $120.6667   $120.67   $120.65   $120.70  
  Purchase #7 $203.33   7.193%   $217.9555   $217.96   $217.95   $218.00  
  7 purchase totals = $1,108.26       $1,207.1494   $1,207.16   $1,207.15   $1,207.20