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 $153.27   11.722%   $171.2363   $171.24   $171.25   $171.20  
  Purchase #2 $248.37   5.632%   $262.3582   $262.36   $262.35   $262.40  
  Purchase #3 $25.27   12.346%   $28.3898   $28.39   $28.40   $28.40  
  Purchase #4 $160.92   11.416%   $179.2906   $179.29   $179.30   $179.30  
  Purchase #5 $219.82   5.801%   $232.5718   $232.57   $232.55   $232.60  
  Purchase #6 $207.53   8.757%   $225.7034   $225.70   $225.70   $225.70  
  Purchase #7 $171.31   3.479%   $177.2699   $177.27   $177.25   $177.30  
  7 purchase totals = $1,186.49       $1,276.8200   $1,276.82   $1,276.80   $1,276.90