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 $46.47   13.391%   $52.6928   $52.69   $52.70   $52.70  
  Purchase #2 $168.37   11.614%   $187.9245   $187.92   $187.90   $187.90  
  Purchase #3 $73.41   7.360%   $78.813   $78.81   $78.80   $78.80  
  Purchase #4 $243.77   3.107%   $251.3439   $251.34   $251.35   $251.30  
  Purchase #5 $22.68   8.102%   $24.5175   $24.52   $24.50   $24.50  
  Purchase #6 $29.32   8.114%   $31.699   $31.70   $31.70   $31.70  
  Purchase #7 $148.28   13.188%   $167.8352   $167.84   $167.85   $167.80  
  7 purchase totals = $732.30       $794.8259   $794.82   $794.80   $794.70