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 $206.60   5.852%   $218.6902   $218.69   $218.70   $218.70  
  Purchase #2 $198.66   5.262%   $209.1135   $209.11   $209.10   $209.10  
  Purchase #3 $63.92   11.142%   $71.042   $71.04   $71.05   $71.00  
  Purchase #4 $39.90   5.166%   $41.9612   $41.96   $41.95   $42.00  
  Purchase #5 $50.93   7.365%   $54.681   $54.68   $54.70   $54.70  
  Purchase #6 $204.67   3.445%   $211.7209   $211.72   $211.70   $211.70  
  Purchase #7 $165.57   7.323%   $177.6947   $177.69   $177.70   $177.70  
  7 purchase totals = $930.25       $984.9035   $984.89   $984.90   $984.90