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 $108.62   8.645%   $118.0102   $118.01   $118.00   $118.00  
  Purchase #2 $23.98   3.784%   $24.8874   $24.89   $24.90   $24.90  
  Purchase #3 $242.59   6.301%   $257.8756   $257.88   $257.90   $257.90  
  Purchase #4 $230.61   10.718%   $255.3268   $255.33   $255.35   $255.30  
  Purchase #5 $228.50   3.132%   $235.6566   $235.66   $235.65   $235.70  
  Purchase #6 $19.86   10.434%   $21.9322   $21.93   $21.95   $21.90  
  Purchase #7 $237.93   3.729%   $246.8024   $246.80   $246.80   $246.80  
  7 purchase totals = $1,092.09       $1,160.4912   $1,160.50   $1,160.55   $1,160.50