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 $10.56   5.653%   $11.157   $11.16   $11.15   $11.20  
  Purchase #2 $214.77   8.861%   $233.8008   $233.80   $233.80   $233.80  
  Purchase #3 $73.49   9.865%   $80.7398   $80.74   $80.75   $80.70  
  Purchase #4 $136.28   6.702%   $145.4135   $145.41   $145.40   $145.40  
  Purchase #5 $103.37   4.280%   $107.7942   $107.79   $107.80   $107.80  
  Purchase #6 $165.77   9.305%   $181.1949   $181.19   $181.20   $181.20  
  Purchase #7 $182.52   6.588%   $194.5444   $194.54   $194.55   $194.50  
  7 purchase totals = $886.76       $954.6446   $954.63   $954.65   $954.60