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 $183.87   10.809%   $203.7445   $203.74   $203.75   $203.70  
  Purchase #2 $59.59   10.519%   $65.8583   $65.86   $65.85   $65.90  
  Purchase #3 $156.62   10.694%   $173.3689   $173.37   $173.35   $173.40  
  Purchase #4 $21.31   12.748%   $24.0266   $24.03   $24.05   $24.00  
  Purchase #5 $142.30   12.691%   $160.3593   $160.36   $160.35   $160.40  
  Purchase #6 $79.25   8.158%   $85.7152   $85.72   $85.70   $85.70  
  Purchase #7 $53.82   12.171%   $60.3704   $60.37   $60.35   $60.40  
  7 purchase totals = $696.76       $773.4432   $773.45   $773.40   $773.50