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 $243.42   10.744%   $269.573   $269.57   $269.55   $269.60  
  Purchase #2 $71.77   3.459%   $74.2525   $74.25   $74.25   $74.30  
  Purchase #3 $97.44   11.833%   $108.9701   $108.97   $108.95   $109.00  
  Purchase #4 $6.37   8.674%   $6.9225   $6.92   $6.90   $6.90  
  Purchase #5 $202.60   8.364%   $219.5455   $219.55   $219.55   $219.50  
  Purchase #6 $173.41   13.516%   $196.8481   $196.85   $196.85   $196.80  
  Purchase #7 $143.40   3.218%   $148.0146   $148.01   $148.00   $148.00  
  7 purchase totals = $938.41       $1,024.1263   $1,024.12   $1,024.05   $1,024.10