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 $226.96   7.390%   $243.7323   $243.73   $243.75   $243.70  
  Purchase #2 $192.59   11.355%   $214.4586   $214.46   $214.45   $214.50  
  Purchase #3 $228.51   11.474%   $254.7292   $254.73   $254.75   $254.70  
  Purchase #4 $100.41   7.136%   $107.5753   $107.58   $107.60   $107.60  
  Purchase #5 $26.76   12.334%   $30.0606   $30.06   $30.05   $30.10  
  Purchase #6 $225.60   13.802%   $256.7373   $256.74   $256.75   $256.70  
  Purchase #7 $151.32   9.362%   $165.4866   $165.49   $165.50   $165.50  
  7 purchase totals = $1,152.15       $1,272.7799   $1,272.79   $1,272.85   $1,272.80