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 $232.65   5.605%   $245.69   $245.69   $245.70   $245.70  
  Purchase #2 $55.89   12.479%   $62.8645   $62.86   $62.85   $62.90  
  Purchase #3 $153.82   12.158%   $172.5214   $172.52   $172.50   $172.50  
  Purchase #4 $28.91   5.325%   $30.4495   $30.45   $30.45   $30.40  
  Purchase #5 $138.29   9.181%   $150.9864   $150.99   $151.00   $151.00  
  Purchase #6 $96.80   10.436%   $106.902   $106.90   $106.90   $106.90  
  Purchase #7 $127.86   9.557%   $140.0796   $140.08   $140.10   $140.10  
  7 purchase totals = $834.22       $909.4934   $909.49   $909.50   $909.50