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 $78.98   9.542%   $86.5163   $86.52   $86.50   $86.50  
  Purchase #2 $116.97   13.408%   $132.6533   $132.65   $132.65   $132.70  
  Purchase #3 $88.33   8.322%   $95.6808   $95.68   $95.70   $95.70  
  Purchase #4 $147.51   4.391%   $153.9872   $153.99   $154.00   $154.00  
  Purchase #5 $212.37   10.872%   $235.4589   $235.46   $235.45   $235.50  
  Purchase #6 $130.99   8.866%   $142.6036   $142.60   $142.60   $142.60  
  Purchase #7 $161.99   5.580%   $171.029   $171.03   $171.05   $171.00  
  7 purchase totals = $937.14       $1,017.9291   $1,017.93   $1,017.95   $1,018.00