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 $217.33   9.788%   $238.6023   $238.60   $238.60   $238.60  
  Purchase #2 $226.25   3.738%   $234.7072   $234.71   $234.70   $234.70  
  Purchase #3 $163.75   5.253%   $172.3518   $172.35   $172.35   $172.40  
  Purchase #4 $204.55   3.693%   $212.104   $212.10   $212.10   $212.10  
  Purchase #5 $24.29   11.171%   $27.0034   $27.00   $27.00   $27.00  
  Purchase #6 $86.91   4.640%   $90.9426   $90.94   $90.95   $90.90  
  Purchase #7 $188.46   5.812%   $199.4133   $199.41   $199.40   $199.40  
  7 purchase totals = $1,111.54       $1,175.1246   $1,175.11   $1,175.10   $1,175.10