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 $93.96   9.107%   $102.5169   $102.52   $102.50   $102.50  
  Purchase #2 $158.79   10.655%   $175.7091   $175.71   $175.70   $175.70  
  Purchase #3 $214.89   9.456%   $235.21   $235.21   $235.20   $235.20  
  Purchase #4 $214.94   9.138%   $234.5812   $234.58   $234.60   $234.60  
  Purchase #5 $14.28   12.523%   $16.0683   $16.07   $16.05   $16.10  
  Purchase #6 $23.59   3.299%   $24.3682   $24.37   $24.35   $24.40  
  Purchase #7 $166.72   7.533%   $179.279   $179.28   $179.30   $179.30  
  7 purchase totals = $887.17       $967.7327   $967.74   $967.70   $967.80