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 $62.30   13.603%   $70.7747   $70.77   $70.75   $70.80  
  Purchase #2 $175.28   7.742%   $188.8502   $188.85   $188.85   $188.90  
  Purchase #3 $24.71   4.797%   $25.8953   $25.90   $25.90   $25.90  
  Purchase #4 $174.99   3.610%   $181.3071   $181.31   $181.30   $181.30  
  Purchase #5 $196.81   10.772%   $218.0104   $218.01   $218.00   $218.00  
  Purchase #6 $53.94   8.633%   $58.5966   $58.60   $58.60   $58.60  
  Purchase #7 $39.44   3.109%   $40.6662   $40.67   $40.65   $40.70  
  7 purchase totals = $727.47       $784.1005   $784.11   $784.05   $784.20