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 $69.65   11.437%   $77.6159   $77.62   $77.60   $77.60  
  Purchase #2 $213.26   11.268%   $237.2901   $237.29   $237.30   $237.30  
  Purchase #3 $100.60   9.615%   $110.2727   $110.27   $110.25   $110.30  
  Purchase #4 $79.34   7.690%   $85.4412   $85.44   $85.45   $85.40  
  Purchase #5 $221.93   10.872%   $246.0582   $246.06   $246.05   $246.10  
  Purchase #6 $57.65   11.220%   $64.1183   $64.12   $64.10   $64.10  
  Purchase #7 $74.62   3.434%   $77.1825   $77.18   $77.20   $77.20  
  7 purchase totals = $817.05       $897.9789   $897.98   $897.95   $898.00