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 $116.94   12.244%   $131.2581   $131.26   $131.25   $131.30  
  Purchase #2 $180.47   8.171%   $195.2162   $195.22   $195.20   $195.20  
  Purchase #3 $191.69   4.656%   $200.6151   $200.62   $200.60   $200.60  
  Purchase #4 $88.83   7.364%   $95.3714   $95.37   $95.35   $95.40  
  Purchase #5 $227.36   3.654%   $235.6677   $235.67   $235.65   $235.70  
  Purchase #6 $102.90   7.300%   $110.4117   $110.41   $110.40   $110.40  
  Purchase #7 $35.83   4.738%   $37.5276   $37.53   $37.55   $37.50  
  7 purchase totals = $944.02       $1,006.0678   $1,006.08   $1,006.00   $1,006.10