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 $203.66   8.753%   $221.4864   $221.49   $221.50   $221.50  
  Purchase #2 $61.97   11.638%   $69.1821   $69.18   $69.20   $69.20  
  Purchase #3 $41.52   12.848%   $46.8545   $46.85   $46.85   $46.90  
  Purchase #4 $176.58   11.861%   $197.5242   $197.52   $197.50   $197.50  
  Purchase #5 $191.89   10.252%   $211.5626   $211.56   $211.55   $211.60  
  Purchase #6 $224.49   10.262%   $247.5272   $247.53   $247.55   $247.50  
  Purchase #7 $107.92   5.447%   $113.7984   $113.80   $113.80   $113.80  
  7 purchase totals = $1,008.03       $1,107.9354   $1,107.93   $1,107.95   $1,108.00