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 $49.99   8.622%   $54.3001   $54.30   $54.30   $54.30  
  Purchase #2 $102.92   3.637%   $106.6632   $106.66   $106.65   $106.70  
  Purchase #3 $237.67   9.315%   $259.809   $259.81   $259.80   $259.80  
  Purchase #4 $169.81   13.183%   $192.1961   $192.20   $192.20   $192.20  
  Purchase #5 $126.89   12.844%   $143.1878   $143.19   $143.20   $143.20  
  Purchase #6 $95.59   13.174%   $108.183   $108.18   $108.20   $108.20  
  Purchase #7 $133.93   8.758%   $145.6596   $145.66   $145.65   $145.70  
  7 purchase totals = $916.80       $1,009.9988   $1,010.00   $1,010.00   $1,010.10