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 $24.84   8.322%   $26.9072   $26.91   $26.90   $26.90  
  Purchase #2 $212.92   10.544%   $235.3703   $235.37   $235.35   $235.40  
  Purchase #3 $133.69   6.338%   $142.1633   $142.16   $142.15   $142.20  
  Purchase #4 $112.45   11.773%   $125.6887   $125.69   $125.70   $125.70  
  Purchase #5 $164.52   11.495%   $183.4316   $183.43   $183.45   $183.40  
  Purchase #6 $184.89   12.238%   $207.5168   $207.52   $207.50   $207.50  
  Purchase #7 $147.67   8.659%   $160.4567   $160.46   $160.45   $160.50  
  7 purchase totals = $980.98       $1,081.5346   $1,081.54   $1,081.50   $1,081.60