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 $247.59   7.734%   $266.7386   $266.74   $266.75   $266.70  
  Purchase #2 $139.69   11.717%   $156.0575   $156.06   $156.05   $156.10  
  Purchase #3 $97.27   13.502%   $110.4034   $110.40   $110.40   $110.40  
  Purchase #4 $87.70   7.255%   $94.0626   $94.06   $94.05   $94.10  
  Purchase #5 $201.79   12.193%   $226.3943   $226.39   $226.40   $226.40  
  Purchase #6 $80.53   13.377%   $91.3025   $91.30   $91.30   $91.30  
  Purchase #7 $96.96   10.177%   $106.8276   $106.83   $106.85   $106.80  
  7 purchase totals = $951.53       $1,051.7865   $1,051.78   $1,051.80   $1,051.80