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 $201.29   3.589%   $208.5143   $208.51   $208.50   $208.50  
  Purchase #2 $67.40   5.414%   $71.049   $71.05   $71.05   $71.00  
  Purchase #3 $49.60   8.302%   $53.7178   $53.72   $53.70   $53.70  
  Purchase #4 $173.97   8.585%   $188.9053   $188.91   $188.90   $188.90  
  Purchase #5 $87.79   9.648%   $96.26   $96.26   $96.25   $96.30  
  Purchase #6 $226.65   3.770%   $235.1947   $235.19   $235.20   $235.20  
  Purchase #7 $185.56   8.164%   $200.7091   $200.71   $200.70   $200.70  
  7 purchase totals = $992.26       $1,054.3502   $1,054.35   $1,054.30   $1,054.30