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 $147.56   9.631%   $161.7715   $161.77   $161.75   $161.80  
  Purchase #2 $75.59   8.103%   $81.7151   $81.72   $81.70   $81.70  
  Purchase #3 $18.50   8.481%   $20.069   $20.07   $20.05   $20.10  
  Purchase #4 $188.30   3.331%   $194.5723   $194.57   $194.55   $194.60  
  Purchase #5 $189.99   7.352%   $203.9581   $203.96   $203.95   $204.00  
  Purchase #6 $126.43   3.745%   $131.1648   $131.16   $131.15   $131.20  
  Purchase #7 $222.79   4.274%   $232.312   $232.31   $232.30   $232.30  
  7 purchase totals = $969.16       $1,025.5628   $1,025.56   $1,025.45   $1,025.70