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 $53.42   6.265%   $56.7668   $56.77   $56.75   $56.80  
  Purchase #2 $93.40   5.313%   $98.3623   $98.36   $98.35   $98.40  
  Purchase #3 $212.78   4.854%   $223.1083   $223.11   $223.10   $223.10  
  Purchase #4 $87.46   6.378%   $93.0382   $93.04   $93.05   $93.00  
  Purchase #5 $232.84   8.839%   $253.4207   $253.42   $253.40   $253.40  
  Purchase #6 $95.49   3.814%   $99.132   $99.13   $99.15   $99.10  
  Purchase #7 $44.91   12.835%   $50.6742   $50.67   $50.65   $50.70  
  7 purchase totals = $820.30       $874.5025   $874.50   $874.45   $874.50