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 $82.83   11.782%   $92.589   $92.59   $92.60   $92.60  
  Purchase #2 $31.50   7.649%   $33.9094   $33.91   $33.90   $33.90  
  Purchase #3 $149.27   6.288%   $158.6561   $158.66   $158.65   $158.70  
  Purchase #4 $76.94   4.291%   $80.2415   $80.24   $80.25   $80.20  
  Purchase #5 $202.90   12.829%   $228.93   $228.93   $228.95   $228.90  
  Purchase #6 $113.82   3.107%   $117.3564   $117.36   $117.35   $117.40  
  Purchase #7 $109.55   13.181%   $123.9898   $123.99   $124.00   $124.00  
  7 purchase totals = $766.81       $835.6722   $835.68   $835.70   $835.70