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 $157.87   10.408%   $174.3011   $174.30   $174.30   $174.30  
  Purchase #2 $219.38   6.589%   $233.8349   $233.83   $233.85   $233.80  
  Purchase #3 $57.35   8.454%   $62.1984   $62.20   $62.20   $62.20  
  Purchase #4 $232.51   4.863%   $243.817   $243.82   $243.80   $243.80  
  Purchase #5 $10.47   7.241%   $11.2281   $11.23   $11.25   $11.20  
  Purchase #6 $151.89   12.650%   $171.1041   $171.10   $171.10   $171.10  
  Purchase #7 $191.99   11.352%   $213.7847   $213.78   $213.80   $213.80  
  7 purchase totals = $1,021.46       $1,110.2683   $1,110.26   $1,110.30   $1,110.20