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 $77.39   8.144%   $83.6926   $83.69   $83.70   $83.70  
  Purchase #2 $227.31   13.483%   $257.9582   $257.96   $257.95   $258.00  
  Purchase #3 $19.52   11.250%   $21.716   $21.72   $21.70   $21.70  
  Purchase #4 $177.80   13.799%   $202.3346   $202.33   $202.35   $202.30  
  Purchase #5 $119.56   4.429%   $124.8553   $124.86   $124.85   $124.90  
  Purchase #6 $245.30   10.438%   $270.9044   $270.90   $270.90   $270.90  
  Purchase #7 $99.79   6.653%   $106.429   $106.43   $106.45   $106.40  
  7 purchase totals = $966.67       $1,067.8901   $1,067.89   $1,067.90   $1,067.90