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 $50.88   5.789%   $53.8254   $53.83   $53.85   $53.80  
  Purchase #2 $229.72   8.243%   $248.6558   $248.66   $248.65   $248.70  
  Purchase #3 $85.72   9.666%   $94.0057   $94.01   $94.00   $94.00  
  Purchase #4 $234.81   5.128%   $246.8511   $246.85   $246.85   $246.90  
  Purchase #5 $11.48   11.292%   $12.7763   $12.78   $12.80   $12.80  
  Purchase #6 $246.71   3.267%   $254.77   $254.77   $254.75   $254.80  
  Purchase #7 $198.67   3.155%   $204.938   $204.94   $204.95   $204.90  
  7 purchase totals = $1,057.99       $1,115.8223   $1,115.84   $1,115.85   $1,115.90