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 $226.54   6.389%   $241.0136   $241.01   $241.00   $241.00  
  Purchase #2 $155.56   9.691%   $170.6353   $170.64   $170.65   $170.60  
  Purchase #3 $226.48   11.323%   $252.1243   $252.12   $252.10   $252.10  
  Purchase #4 $106.41   3.567%   $110.2056   $110.21   $110.20   $110.20  
  Purchase #5 $226.67   4.567%   $237.022   $237.02   $237.00   $237.00  
  Purchase #6 $12.90   11.218%   $14.3471   $14.35   $14.35   $14.30  
  Purchase #7 $94.52   12.264%   $106.1119   $106.11   $106.10   $106.10  
  7 purchase totals = $1,049.08       $1,131.4598   $1,131.46   $1,131.40   $1,131.30