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 $171.92   7.418%   $184.673   $184.67   $184.65   $184.70  
  Purchase #2 $198.39   9.848%   $217.9274   $217.93   $217.95   $217.90  
  Purchase #3 $219.95   4.583%   $230.0303   $230.03   $230.05   $230.00  
  Purchase #4 $55.31   12.646%   $62.3045   $62.30   $62.30   $62.30  
  Purchase #5 $117.84   3.567%   $122.0434   $122.04   $122.05   $122.00  
  Purchase #6 $182.65   11.269%   $203.2328   $203.23   $203.25   $203.20  
  Purchase #7 $163.27   5.821%   $172.7739   $172.77   $172.75   $172.80  
  7 purchase totals = $1,109.33       $1,192.9853   $1,192.97   $1,193.00   $1,192.90