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 $65.84   7.559%   $70.8168   $70.82   $70.80   $70.80  
  Purchase #2 $183.50   10.646%   $203.0354   $203.04   $203.05   $203.00  
  Purchase #3 $141.99   6.751%   $151.5757   $151.58   $151.60   $151.60  
  Purchase #4 $112.47   12.550%   $126.585   $126.59   $126.60   $126.60  
  Purchase #5 $163.58   7.531%   $175.8992   $175.90   $175.90   $175.90  
  Purchase #6 $149.99   4.478%   $156.7066   $156.71   $156.70   $156.70  
  Purchase #7 $36.98   6.472%   $39.3733   $39.37   $39.35   $39.40  
  7 purchase totals = $854.35       $923.9920   $924.01   $924.00   $924.00