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 $64.99   12.621%   $73.1924   $73.19   $73.20   $73.20  
  Purchase #2 $250.92   6.297%   $266.7204   $266.72   $266.70   $266.70  
  Purchase #3 $79.73   9.513%   $87.3147   $87.31   $87.30   $87.30  
  Purchase #4 $59.43   8.651%   $64.5713   $64.57   $64.55   $64.60  
  Purchase #5 $242.52   4.659%   $253.819   $253.82   $253.80   $253.80  
  Purchase #6 $133.32   13.325%   $151.0849   $151.08   $151.10   $151.10  
  Purchase #7 $7.68   4.642%   $8.0365   $8.04   $8.05   $8.00  
  7 purchase totals = $838.59       $904.7392   $904.73   $904.70   $904.70