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 $53.33   5.840%   $56.4445   $56.44   $56.45   $56.40  
  Purchase #2 $11.57   5.279%   $12.1808   $12.18   $12.20   $12.20  
  Purchase #3 $16.73   11.591%   $18.6692   $18.67   $18.65   $18.70  
  Purchase #4 $229.82   5.336%   $242.0832   $242.08   $242.10   $242.10  
  Purchase #5 $247.33   4.289%   $257.938   $257.94   $257.95   $257.90  
  Purchase #6 $183.31   7.285%   $196.6641   $196.66   $196.65   $196.70  
  Purchase #7 $181.37   5.845%   $191.9711   $191.97   $191.95   $192.00  
  7 purchase totals = $923.46       $975.9509   $975.94   $975.95   $976.00