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 $218.92   3.505%   $226.5931   $226.59   $226.60   $226.60  
  Purchase #2 $223.25   11.535%   $249.0019   $249.00   $249.00   $249.00  
  Purchase #3 $22.31   4.288%   $23.2667   $23.27   $23.25   $23.30  
  Purchase #4 $202.45   12.407%   $227.568   $227.57   $227.55   $227.60  
  Purchase #5 $221.78   12.424%   $249.3339   $249.33   $249.35   $249.30  
  Purchase #6 $221.98   11.180%   $246.7974   $246.80   $246.80   $246.80  
  Purchase #7 $234.33   12.402%   $263.3916   $263.39   $263.40   $263.40  
  7 purchase totals = $1,345.02       $1,485.9526   $1,485.95   $1,485.95   $1,486.00