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 $152.48   9.537%   $167.022   $167.02   $167.00   $167.00  
  Purchase #2 $62.48   13.646%   $71.006   $71.01   $71.00   $71.00  
  Purchase #3 $250.92   6.842%   $268.0879   $268.09   $268.10   $268.10  
  Purchase #4 $108.95   3.414%   $112.6696   $112.67   $112.65   $112.70  
  Purchase #5 $93.61   6.212%   $99.4251   $99.43   $99.45   $99.40  
  Purchase #6 $27.72   10.294%   $30.5735   $30.57   $30.55   $30.60  
  Purchase #7 $218.63   12.795%   $246.6037   $246.60   $246.60   $246.60  
  7 purchase totals = $914.79       $995.3878   $995.39   $995.35   $995.40