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 $246.57   6.644%   $262.9521   $262.95   $262.95   $263.00  
  Purchase #2 $227.71   5.486%   $240.2022   $240.20   $240.20   $240.20  
  Purchase #3 $141.83   7.430%   $152.368   $152.37   $152.35   $152.40  
  Purchase #4 $138.45   11.181%   $153.9301   $153.93   $153.95   $153.90  
  Purchase #5 $180.33   6.666%   $192.3508   $192.35   $192.35   $192.40  
  Purchase #6 $179.57   12.226%   $201.5242   $201.52   $201.50   $201.50  
  Purchase #7 $56.36   4.388%   $58.8331   $58.83   $58.85   $58.80  
  7 purchase totals = $1,170.82       $1,262.1605   $1,262.15   $1,262.15   $1,262.20