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 $89.66   4.802%   $93.9655   $93.97   $93.95   $94.00  
  Purchase #2 $66.51   12.187%   $74.6156   $74.62   $74.60   $74.60  
  Purchase #3 $127.67   7.745%   $137.558   $137.56   $137.55   $137.60  
  Purchase #4 $207.46   9.446%   $227.0567   $227.06   $227.05   $227.10  
  Purchase #5 $174.59   12.743%   $196.838   $196.84   $196.85   $196.80  
  Purchase #6 $140.78   4.791%   $147.5248   $147.52   $147.50   $147.50  
  Purchase #7 $158.66   10.107%   $174.6958   $174.70   $174.70   $174.70  
  7 purchase totals = $965.33       $1,052.2544   $1,052.27   $1,052.20   $1,052.30