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 $52.44   13.533%   $59.5367   $59.54   $59.55   $59.50  
  Purchase #2 $80.31   5.784%   $84.9551   $84.96   $84.95   $85.00  
  Purchase #3 $223.35   10.415%   $246.6119   $246.61   $246.60   $246.60  
  Purchase #4 $167.72   5.843%   $177.5199   $177.52   $177.50   $177.50  
  Purchase #5 $100.68   5.523%   $106.2406   $106.24   $106.25   $106.20  
  Purchase #6 $28.69   10.587%   $31.7274   $31.73   $31.75   $31.70  
  Purchase #7 $233.39   8.246%   $252.6353   $252.64   $252.65   $252.60  
  7 purchase totals = $886.58       $959.2269   $959.24   $959.25   $959.10