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 $150.74   12.123%   $169.0142   $169.01   $169.00   $169.00  
  Purchase #2 $66.50   13.397%   $75.409   $75.41   $75.40   $75.40  
  Purchase #3 $58.77   11.104%   $65.2958   $65.30   $65.30   $65.30  
  Purchase #4 $216.36   4.841%   $226.834   $226.83   $226.85   $226.80  
  Purchase #5 $54.73   3.118%   $56.4365   $56.44   $56.45   $56.40  
  Purchase #6 $246.76   12.358%   $277.2546   $277.25   $277.25   $277.30  
  Purchase #7 $172.54   8.825%   $187.7667   $187.77   $187.75   $187.80  
  7 purchase totals = $966.40       $1,058.0108   $1,058.01   $1,058.00   $1,058.00