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 $89.25   8.477%   $96.8157   $96.82   $96.80   $96.80  
  Purchase #2 $213.66   9.143%   $233.1949   $233.19   $233.20   $233.20  
  Purchase #3 $181.67   11.557%   $202.6656   $202.67   $202.65   $202.70  
  Purchase #4 $54.84   11.318%   $61.0468   $61.05   $61.05   $61.00  
  Purchase #5 $70.39   3.116%   $72.5834   $72.58   $72.60   $72.60  
  Purchase #6 $21.52   6.263%   $22.8678   $22.87   $22.85   $22.90  
  Purchase #7 $192.64   3.818%   $199.995   $200.00   $200.00   $200.00  
  7 purchase totals = $823.97       $889.1692   $889.18   $889.15   $889.20