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 $7.46   8.273%   $8.0772   $8.08   $8.10   $8.10  
  Purchase #2 $222.85   5.168%   $234.3669   $234.37   $234.35   $234.40  
  Purchase #3 $250.67   10.384%   $276.6996   $276.70   $276.70   $276.70  
  Purchase #4 $181.78   5.842%   $192.3996   $192.40   $192.40   $192.40  
  Purchase #5 $64.48   13.515%   $73.1945   $73.19   $73.20   $73.20  
  Purchase #6 $120.32   4.514%   $125.7512   $125.75   $125.75   $125.80  
  Purchase #7 $141.42   6.209%   $150.2008   $150.20   $150.20   $150.20  
  7 purchase totals = $988.98       $1,060.6898   $1,060.69   $1,060.70   $1,060.80