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 $62.29   5.130%   $65.4855   $65.49   $65.50   $65.50  
  Purchase #2 $14.93   11.836%   $16.6971   $16.70   $16.70   $16.70  
  Purchase #3 $134.51   3.179%   $138.7861   $138.79   $138.80   $138.80  
  Purchase #4 $202.39   3.410%   $209.2915   $209.29   $209.30   $209.30  
  Purchase #5 $171.85   9.652%   $188.437   $188.44   $188.45   $188.40  
  Purchase #6 $197.60   12.523%   $222.3454   $222.35   $222.35   $222.30  
  Purchase #7 $204.50   10.461%   $225.8927   $225.89   $225.90   $225.90  
  7 purchase totals = $988.07       $1,066.9353   $1,066.95   $1,067.00   $1,066.90