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 $244.56   9.365%   $267.463   $267.46   $267.45   $267.50  
  Purchase #2 $82.43   13.308%   $93.3998   $93.40   $93.40   $93.40  
  Purchase #3 $70.64   9.643%   $77.4518   $77.45   $77.45   $77.50  
  Purchase #4 $14.46   11.818%   $16.1689   $16.17   $16.15   $16.20  
  Purchase #5 $6.28   12.787%   $7.083   $7.08   $7.10   $7.10  
  Purchase #6 $212.69   13.538%   $241.484   $241.48   $241.50   $241.50  
  Purchase #7 $231.62   6.714%   $247.171   $247.17   $247.15   $247.20  
  7 purchase totals = $862.68       $950.2215   $950.21   $950.20   $950.40