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 $33.47   8.565%   $36.3367   $36.34   $36.35   $36.30  
  Purchase #2 $102.54   6.753%   $109.4645   $109.46   $109.45   $109.50  
  Purchase #3 $244.90   7.153%   $262.4177   $262.42   $262.40   $262.40  
  Purchase #4 $75.52   8.656%   $82.057   $82.06   $82.05   $82.10  
  Purchase #5 $151.48   12.655%   $170.6498   $170.65   $170.65   $170.60  
  Purchase #6 $205.30   5.136%   $215.8442   $215.84   $215.85   $215.80  
  Purchase #7 $181.80   13.746%   $206.7902   $206.79   $206.80   $206.80  
  7 purchase totals = $995.01       $1,083.5601   $1,083.56   $1,083.55   $1,083.50