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 $88.26   4.444%   $92.1823   $92.18   $92.20   $92.20  
  Purchase #2 $56.52   10.851%   $62.653   $62.65   $62.65   $62.70  
  Purchase #3 $71.46   12.113%   $80.1159   $80.12   $80.10   $80.10  
  Purchase #4 $201.61   6.236%   $214.1824   $214.18   $214.20   $214.20  
  Purchase #5 $221.79   9.868%   $243.6762   $243.68   $243.70   $243.70  
  Purchase #6 $146.30   3.750%   $151.7863   $151.79   $151.80   $151.80  
  Purchase #7 $173.65   7.402%   $186.5036   $186.50   $186.50   $186.50  
  7 purchase totals = $959.59       $1,031.0997   $1,031.10   $1,031.15   $1,031.20