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 $162.60   5.611%   $171.7235   $171.72   $171.70   $171.70  
  Purchase #2 $45.66   7.113%   $48.9078   $48.91   $48.90   $48.90  
  Purchase #3 $220.63   5.766%   $233.3515   $233.35   $233.35   $233.40  
  Purchase #4 $180.28   9.792%   $197.933   $197.93   $197.95   $197.90  
  Purchase #5 $149.84   10.458%   $165.5103   $165.51   $165.50   $165.50  
  Purchase #6 $147.40   13.270%   $166.96   $166.96   $166.95   $167.00  
  Purchase #7 $61.77   6.217%   $65.6102   $65.61   $65.60   $65.60  
  7 purchase totals = $968.18       $1,049.9963   $1,049.99   $1,049.95   $1,050.00