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 $73.83   11.532%   $82.3441   $82.34   $82.35   $82.30  
  Purchase #2 $118.97   4.779%   $124.6556   $124.66   $124.65   $124.70  
  Purchase #3 $71.48   5.264%   $75.2427   $75.24   $75.25   $75.20  
  Purchase #4 $112.80   13.168%   $127.6535   $127.65   $127.65   $127.70  
  Purchase #5 $220.59   7.506%   $237.1475   $237.15   $237.15   $237.10  
  Purchase #6 $169.47   13.850%   $192.9416   $192.94   $192.95   $192.90  
  Purchase #7 $99.78   7.280%   $107.044   $107.04   $107.05   $107.00  
  7 purchase totals = $866.92       $947.0290   $947.02   $947.05   $946.90