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 $202.42   13.617%   $229.9835   $229.98   $230.00   $230.00  
  Purchase #2 $7.31   12.128%   $8.1966   $8.20   $8.20   $8.20  
  Purchase #3 $25.80   3.661%   $26.7445   $26.74   $26.75   $26.70  
  Purchase #4 $57.96   6.374%   $61.6544   $61.65   $61.65   $61.70  
  Purchase #5 $94.66   12.303%   $106.306   $106.31   $106.30   $106.30  
  Purchase #6 $225.63   4.556%   $235.9097   $235.91   $235.90   $235.90  
  Purchase #7 $78.70   10.790%   $87.1917   $87.19   $87.20   $87.20  
  7 purchase totals = $692.48       $755.9864   $755.98   $756.00   $756.00