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 $80.66   13.197%   $91.3047   $91.30   $91.30   $91.30  
  Purchase #2 $146.93   12.736%   $165.643   $165.64   $165.65   $165.60  
  Purchase #3 $13.57   4.615%   $14.1963   $14.20   $14.20   $14.20  
  Purchase #4 $87.98   4.504%   $91.9426   $91.94   $91.95   $91.90  
  Purchase #5 $100.36   7.284%   $107.6702   $107.67   $107.65   $107.70  
  Purchase #6 $44.55   11.102%   $49.4959   $49.50   $49.50   $49.50  
  Purchase #7 $245.67   11.212%   $273.2145   $273.21   $273.20   $273.20  
  7 purchase totals = $719.72       $793.4672   $793.46   $793.45   $793.40