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 $246.92   6.737%   $263.555   $263.56   $263.55   $263.60  
  Purchase #2 $137.90   5.335%   $145.257   $145.26   $145.25   $145.30  
  Purchase #3 $214.63   8.399%   $232.6568   $232.66   $232.65   $232.70  
  Purchase #4 $210.82   4.415%   $220.1277   $220.13   $220.15   $220.10  
  Purchase #5 $113.48   8.124%   $122.6991   $122.70   $122.70   $122.70  
  Purchase #6 $241.80   8.803%   $263.0857   $263.09   $263.10   $263.10  
  Purchase #7 $182.79   13.222%   $206.9585   $206.96   $206.95   $207.00  
  7 purchase totals = $1,348.34       $1,454.3398   $1,454.36   $1,454.35   $1,454.50