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 $204.29   6.479%   $217.5259   $217.53   $217.55   $217.50  
  Purchase #2 $86.50   11.349%   $96.3169   $96.32   $96.30   $96.30  
  Purchase #3 $159.35   4.519%   $166.551   $166.55   $166.55   $166.60  
  Purchase #4 $179.61   8.627%   $195.105   $195.11   $195.10   $195.10  
  Purchase #5 $29.85   6.373%   $31.7523   $31.75   $31.75   $31.80  
  Purchase #6 $37.70   11.270%   $41.9488   $41.95   $41.95   $41.90  
  Purchase #7 $243.69   3.483%   $252.1777   $252.18   $252.20   $252.20  
  7 purchase totals = $940.99       $1,001.3776   $1,001.39   $1,001.40   $1,001.40