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 $208.67   10.178%   $229.9084   $229.91   $229.90   $229.90  
  Purchase #2 $40.28   7.651%   $43.3618   $43.36   $43.35   $43.40  
  Purchase #3 $204.61   13.841%   $232.9301   $232.93   $232.95   $232.90  
  Purchase #4 $109.39   10.396%   $120.7622   $120.76   $120.75   $120.80  
  Purchase #5 $198.26   13.461%   $224.9478   $224.95   $224.95   $224.90  
  Purchase #6 $59.73   13.811%   $67.9793   $67.98   $68.00   $68.00  
  Purchase #7 $217.35   7.824%   $234.3555   $234.36   $234.35   $234.40  
  7 purchase totals = $1,038.29       $1,154.2451   $1,154.25   $1,154.25   $1,154.30