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 $48.43   13.433%   $54.9356   $54.94   $54.95   $54.90  
  Purchase #2 $116.95   6.529%   $124.5857   $124.59   $124.60   $124.60  
  Purchase #3 $21.71   7.525%   $23.3437   $23.34   $23.35   $23.30  
  Purchase #4 $232.51   13.377%   $263.6129   $263.61   $263.60   $263.60  
  Purchase #5 $110.85   9.481%   $121.3597   $121.36   $121.35   $121.40  
  Purchase #6 $227.87   11.751%   $254.647   $254.65   $254.65   $254.60  
  Purchase #7 $24.55   13.476%   $27.8584   $27.86   $27.85   $27.90  
  7 purchase totals = $782.87       $870.3430   $870.35   $870.35   $870.30