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 $91.59   7.298%   $98.2742   $98.27   $98.25   $98.30  
  Purchase #2 $86.33   12.690%   $97.2853   $97.29   $97.30   $97.30  
  Purchase #3 $232.40   8.433%   $251.9983   $252.00   $252.00   $252.00  
  Purchase #4 $26.91   7.572%   $28.9476   $28.95   $28.95   $28.90  
  Purchase #5 $136.31   12.453%   $153.2847   $153.28   $153.30   $153.30  
  Purchase #6 $174.26   9.586%   $190.9646   $190.96   $190.95   $191.00  
  Purchase #7 $113.39   6.372%   $120.6152   $120.62   $120.60   $120.60  
  7 purchase totals = $861.19       $941.3699   $941.37   $941.35   $941.40