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 $112.30   12.569%   $126.415   $126.42   $126.40   $126.40  
  Purchase #2 $95.60   5.433%   $100.7939   $100.79   $100.80   $100.80  
  Purchase #3 $207.25   10.700%   $229.4258   $229.43   $229.45   $229.40  
  Purchase #4 $247.72   7.623%   $266.6037   $266.60   $266.60   $266.60  
  Purchase #5 $162.67   3.141%   $167.7795   $167.78   $167.80   $167.80  
  Purchase #6 $99.26   3.828%   $103.0597   $103.06   $103.05   $103.10  
  Purchase #7 $69.25   6.831%   $73.9805   $73.98   $74.00   $74.00  
  7 purchase totals = $994.05       $1,068.0581   $1,068.06   $1,068.10   $1,068.10