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 $187.46   8.157%   $202.7511   $202.75   $202.75   $202.80  
  Purchase #2 $65.79   6.358%   $69.9729   $69.97   $69.95   $70.00  
  Purchase #3 $29.43   12.398%   $33.0787   $33.08   $33.10   $33.10  
  Purchase #4 $241.37   10.509%   $266.7356   $266.74   $266.75   $266.70  
  Purchase #5 $135.48   5.119%   $142.4152   $142.42   $142.40   $142.40  
  Purchase #6 $138.88   9.189%   $151.6417   $151.64   $151.65   $151.60  
  Purchase #7 $152.51   10.247%   $168.1377   $168.14   $168.15   $168.10  
  7 purchase totals = $950.92       $1,034.7329   $1,034.74   $1,034.75   $1,034.70