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 $214.75   7.109%   $230.0166   $230.02   $230.00   $230.00  
  Purchase #2 $237.91   6.567%   $253.5335   $253.53   $253.55   $253.50  
  Purchase #3 $16.68   4.248%   $17.3886   $17.39   $17.40   $17.40  
  Purchase #4 $244.95   8.166%   $264.9526   $264.95   $264.95   $265.00  
  Purchase #5 $167.74   7.149%   $179.7317   $179.73   $179.75   $179.70  
  Purchase #6 $22.98   12.514%   $25.8557   $25.86   $25.85   $25.90  
  Purchase #7 $81.51   7.632%   $87.7308   $87.73   $87.75   $87.70  
  7 purchase totals = $986.52       $1,059.2095   $1,059.21   $1,059.25   $1,059.20