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 $63.28   10.658%   $70.0244   $70.02   $70.00   $70.00  
  Purchase #2 $81.46   6.852%   $87.0416   $87.04   $87.05   $87.00  
  Purchase #3 $87.32   8.505%   $94.7466   $94.75   $94.75   $94.70  
  Purchase #4 $136.81   6.654%   $145.9133   $145.91   $145.90   $145.90  
  Purchase #5 $236.75   9.831%   $260.0249   $260.02   $260.00   $260.00  
  Purchase #6 $176.80   6.485%   $188.2655   $188.27   $188.25   $188.30  
  Purchase #7 $187.31   7.598%   $201.5418   $201.54   $201.55   $201.50  
  7 purchase totals = $969.73       $1,047.5581   $1,047.55   $1,047.50   $1,047.40