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 $241.79   5.392%   $254.8273   $254.83   $254.85   $254.80  
  Purchase #2 $91.54   12.473%   $102.9578   $102.96   $102.95   $103.00  
  Purchase #3 $93.88   12.594%   $105.7032   $105.70   $105.70   $105.70  
  Purchase #4 $89.78   12.107%   $100.6497   $100.65   $100.65   $100.60  
  Purchase #5 $147.92   3.190%   $152.6386   $152.64   $152.65   $152.60  
  Purchase #6 $223.83   12.121%   $250.9604   $250.96   $250.95   $251.00  
  Purchase #7 $246.58   7.504%   $265.0834   $265.08   $265.10   $265.10  
  7 purchase totals = $1,135.32       $1,232.8204   $1,232.82   $1,232.85   $1,232.80