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 $244.49   10.707%   $270.6675   $270.67   $270.65   $270.70  
  Purchase #2 $54.53   12.370%   $61.2754   $61.28   $61.30   $61.30  
  Purchase #3 $155.36   6.218%   $165.0203   $165.02   $165.00   $165.00  
  Purchase #4 $35.44   6.323%   $37.6809   $37.68   $37.70   $37.70  
  Purchase #5 $108.42   10.157%   $119.4322   $119.43   $119.45   $119.40  
  Purchase #6 $224.69   8.223%   $243.1663   $243.17   $243.15   $243.20  
  Purchase #7 $234.67   12.525%   $264.0624   $264.06   $264.05   $264.10  
  7 purchase totals = $1,057.60       $1,161.3050   $1,161.31   $1,161.30   $1,161.40