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 $83.92   9.516%   $91.9058   $91.91   $91.90   $91.90  
  Purchase #2 $58.37   5.495%   $61.5774   $61.58   $61.60   $61.60  
  Purchase #3 $63.57   12.133%   $71.2829   $71.28   $71.30   $71.30  
  Purchase #4 $214.52   4.789%   $224.7934   $224.79   $224.80   $224.80  
  Purchase #5 $84.65   5.596%   $89.387   $89.39   $89.40   $89.40  
  Purchase #6 $183.82   11.361%   $204.7038   $204.70   $204.70   $204.70  
  Purchase #7 $183.37   5.646%   $193.7231   $193.72   $193.70   $193.70  
  7 purchase totals = $872.22       $937.3734   $937.37   $937.40   $937.40