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 $55.84   4.411%   $58.3031   $58.30   $58.30   $58.30  
  Purchase #2 $203.47   5.461%   $214.5815   $214.58   $214.60   $214.60  
  Purchase #3 $85.80   5.152%   $90.2204   $90.22   $90.20   $90.20  
  Purchase #4 $238.45   5.212%   $250.878   $250.88   $250.90   $250.90  
  Purchase #5 $82.50   11.118%   $91.6724   $91.67   $91.65   $91.70  
  Purchase #6 $22.71   6.632%   $24.2161   $24.22   $24.20   $24.20  
  Purchase #7 $5.72   3.281%   $5.9077   $5.91   $5.90   $5.90  
  7 purchase totals = $694.49       $735.7792   $735.78   $735.75   $735.80