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 $84.30   11.108%   $93.664   $93.66   $93.65   $93.70  
  Purchase #2 $218.25   8.334%   $236.439   $236.44   $236.45   $236.40  
  Purchase #3 $104.81   4.772%   $109.8115   $109.81   $109.80   $109.80  
  Purchase #4 $231.65   9.807%   $254.3679   $254.37   $254.35   $254.40  
  Purchase #5 $99.53   7.349%   $106.8445   $106.84   $106.85   $106.80  
  Purchase #6 $188.80   8.179%   $204.242   $204.24   $204.25   $204.20  
  Purchase #7 $246.83   6.829%   $263.686   $263.69   $263.70   $263.70  
  7 purchase totals = $1,174.17       $1,269.0549   $1,269.05   $1,269.05   $1,269.00