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 $232.57   13.111%   $263.0623   $263.06   $263.05   $263.10  
  Purchase #2 $117.46   5.385%   $123.7852   $123.79   $123.80   $123.80  
  Purchase #3 $241.79   4.231%   $252.0201   $252.02   $252.00   $252.00  
  Purchase #4 $81.60   12.559%   $91.8481   $91.85   $91.85   $91.80  
  Purchase #5 $100.82   5.390%   $106.2542   $106.25   $106.25   $106.30  
  Purchase #6 $236.65   4.147%   $246.4639   $246.46   $246.45   $246.50  
  Purchase #7 $150.65   6.563%   $160.5372   $160.54   $160.55   $160.50  
  7 purchase totals = $1,161.54       $1,243.9710   $1,243.97   $1,243.95   $1,244.00