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 $197.85   13.670%   $224.8961   $224.90   $224.90   $224.90  
  Purchase #2 $181.50   9.402%   $198.5646   $198.56   $198.55   $198.60  
  Purchase #3 $88.74   9.646%   $97.2999   $97.30   $97.30   $97.30  
  Purchase #4 $61.88   9.524%   $67.7735   $67.77   $67.75   $67.80  
  Purchase #5 $33.32   3.643%   $34.5338   $34.53   $34.55   $34.50  
  Purchase #6 $215.76   9.158%   $235.5193   $235.52   $235.50   $235.50  
  Purchase #7 $148.96   4.369%   $155.4681   $155.47   $155.45   $155.50  
  7 purchase totals = $928.01       $1,014.0553   $1,014.05   $1,014.00   $1,014.10