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 $91.29   6.194%   $96.9445   $96.94   $96.95   $96.90  
  Purchase #2 $98.52   6.787%   $105.2066   $105.21   $105.20   $105.20  
  Purchase #3 $96.33   12.146%   $108.0302   $108.03   $108.05   $108.00  
  Purchase #4 $249.65   13.322%   $282.9084   $282.91   $282.90   $282.90  
  Purchase #5 $55.84   5.428%   $58.871   $58.87   $58.85   $58.90  
  Purchase #6 $47.62   5.479%   $50.2291   $50.23   $50.25   $50.20  
  Purchase #7 $237.92   8.378%   $257.8529   $257.85   $257.85   $257.90  
  7 purchase totals = $877.17       $960.0427   $960.04   $960.05   $960.00