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 $194.30   5.363%   $204.7203   $204.72   $204.70   $204.70  
  Purchase #2 $50.36   12.255%   $56.5316   $56.53   $56.55   $56.50  
  Purchase #3 $26.37   13.614%   $29.96   $29.96   $29.95   $30.00  
  Purchase #4 $124.36   11.747%   $138.9686   $138.97   $138.95   $139.00  
  Purchase #5 $219.52   10.635%   $242.866   $242.87   $242.85   $242.90  
  Purchase #6 $169.59   10.462%   $187.3325   $187.33   $187.35   $187.30  
  Purchase #7 $120.72   10.671%   $133.602   $133.60   $133.60   $133.60  
  7 purchase totals = $905.22       $993.9810   $993.98   $993.95   $994.00