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 $61.33   7.116%   $65.6942   $65.69   $65.70   $65.70  
  Purchase #2 $50.57   9.155%   $55.1997   $55.20   $55.20   $55.20  
  Purchase #3 $226.49   12.374%   $254.5159   $254.52   $254.50   $254.50  
  Purchase #4 $169.25   7.318%   $181.6357   $181.64   $181.65   $181.60  
  Purchase #5 $200.78   8.407%   $217.6596   $217.66   $217.65   $217.70  
  Purchase #6 $224.90   8.752%   $244.5832   $244.58   $244.60   $244.60  
  Purchase #7 $91.86   3.778%   $95.3305   $95.33   $95.35   $95.30  
  7 purchase totals = $1,025.18       $1,114.6188   $1,114.62   $1,114.65   $1,114.60