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 $186.95   13.310%   $211.833   $211.83   $211.85   $211.80  
  Purchase #2 $55.97   13.815%   $63.7023   $63.70   $63.70   $63.70  
  Purchase #3 $204.46   9.399%   $223.6772   $223.68   $223.70   $223.70  
  Purchase #4 $240.60   5.284%   $253.3133   $253.31   $253.30   $253.30  
  Purchase #5 $133.47   10.482%   $147.4603   $147.46   $147.45   $147.50  
  Purchase #6 $65.90   5.443%   $69.4869   $69.49   $69.50   $69.50  
  Purchase #7 $22.53   3.235%   $23.2588   $23.26   $23.25   $23.30  
  7 purchase totals = $909.88       $992.7318   $992.73   $992.75   $992.80