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 $232.26   4.142%   $241.8802   $241.88   $241.90   $241.90  
  Purchase #2 $66.77   13.308%   $75.6558   $75.66   $75.65   $75.70  
  Purchase #3 $13.59   6.162%   $14.4274   $14.43   $14.45   $14.40  
  Purchase #4 $69.27   6.661%   $73.8841   $73.88   $73.90   $73.90  
  Purchase #5 $129.25   13.841%   $147.1395   $147.14   $147.15   $147.10  
  Purchase #6 $118.82   6.723%   $126.8083   $126.81   $126.80   $126.80  
  Purchase #7 $24.72   4.758%   $25.8962   $25.90   $25.90   $25.90  
  7 purchase totals = $654.68       $705.6915   $705.70   $705.75   $705.70