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 $49.41   7.684%   $53.2067   $53.21   $53.20   $53.20  
  Purchase #2 $201.78   6.521%   $214.9381   $214.94   $214.95   $214.90  
  Purchase #3 $241.29   6.501%   $256.9763   $256.98   $257.00   $257.00  
  Purchase #4 $222.84   10.174%   $245.5117   $245.51   $245.50   $245.50  
  Purchase #5 $156.75   3.702%   $162.5529   $162.55   $162.55   $162.60  
  Purchase #6 $53.37   10.291%   $58.8623   $58.86   $58.85   $58.90  
  Purchase #7 $202.88   3.338%   $209.6521   $209.65   $209.65   $209.70  
  7 purchase totals = $1,128.32       $1,201.7001   $1,201.70   $1,201.70   $1,201.80