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 $150.91   11.683%   $168.5408   $168.54   $168.55   $168.50  
  Purchase #2 $111.80   10.333%   $123.3523   $123.35   $123.35   $123.40  
  Purchase #3 $74.79   10.552%   $82.6818   $82.68   $82.70   $82.70  
  Purchase #4 $229.73   7.427%   $246.792   $246.79   $246.80   $246.80  
  Purchase #5 $214.73   12.227%   $240.985   $240.99   $241.00   $241.00  
  Purchase #6 $235.37   13.608%   $267.3991   $267.40   $267.40   $267.40  
  Purchase #7 $118.84   3.162%   $122.5977   $122.60   $122.60   $122.60  
  7 purchase totals = $1,136.17       $1,252.3487   $1,252.35   $1,252.40   $1,252.40