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 $250.56   3.832%   $260.1615   $260.16   $260.15   $260.20  
  Purchase #2 $44.31   11.286%   $49.3108   $49.31   $49.30   $49.30  
  Purchase #3 $128.72   9.573%   $141.0424   $141.04   $141.05   $141.00  
  Purchase #4 $154.87   7.535%   $166.5395   $166.54   $166.55   $166.50  
  Purchase #5 $198.33   9.281%   $216.737   $216.74   $216.75   $216.70  
  Purchase #6 $209.27   12.523%   $235.4769   $235.48   $235.50   $235.50  
  Purchase #7 $31.91   7.332%   $34.2496   $34.25   $34.25   $34.20  
  7 purchase totals = $1,017.97       $1,103.5177   $1,103.52   $1,103.55   $1,103.40