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 $179.69   9.470%   $196.7066   $196.71   $196.70   $196.70  
  Purchase #2 $82.59   12.623%   $93.0153   $93.02   $93.00   $93.00  
  Purchase #3 $244.68   13.133%   $276.8138   $276.81   $276.80   $276.80  
  Purchase #4 $188.98   4.764%   $197.983   $197.98   $198.00   $198.00  
  Purchase #5 $53.52   5.202%   $56.3041   $56.30   $56.30   $56.30  
  Purchase #6 $222.44   9.594%   $243.7809   $243.78   $243.80   $243.80  
  Purchase #7 $153.37   10.447%   $169.3926   $169.39   $169.40   $169.40  
  7 purchase totals = $1,125.27       $1,233.9963   $1,233.99   $1,234.00   $1,234.00