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 $153.83   5.767%   $162.7014   $162.70   $162.70   $162.70  
  Purchase #2 $64.97   12.481%   $73.0789   $73.08   $73.10   $73.10  
  Purchase #3 $25.88   13.352%   $29.3355   $29.34   $29.35   $29.30  
  Purchase #4 $14.81   13.835%   $16.859   $16.86   $16.85   $16.90  
  Purchase #5 $56.52   9.108%   $61.6678   $61.67   $61.65   $61.70  
  Purchase #6 $238.52   5.279%   $251.1115   $251.11   $251.10   $251.10  
  Purchase #7 $196.48   4.767%   $205.8462   $205.85   $205.85   $205.80  
  7 purchase totals = $751.01       $800.6003   $800.61   $800.60   $800.60