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 $230.95   9.196%   $252.1882   $252.19   $252.20   $252.20  
  Purchase #2 $116.48   5.417%   $122.7897   $122.79   $122.80   $122.80  
  Purchase #3 $38.36   7.456%   $41.2201   $41.22   $41.20   $41.20  
  Purchase #4 $201.27   9.781%   $220.9562   $220.96   $220.95   $221.00  
  Purchase #5 $86.37   8.483%   $93.6968   $93.70   $93.70   $93.70  
  Purchase #6 $58.72   11.177%   $65.2831   $65.28   $65.30   $65.30  
  Purchase #7 $192.90   6.671%   $205.7684   $205.77   $205.75   $205.80  
  7 purchase totals = $925.05       $1,001.9025   $1,001.91   $1,001.90   $1,002.00