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 $74.67   3.471%   $77.2618   $77.26   $77.25   $77.30  
  Purchase #2 $96.72   7.365%   $103.8434   $103.84   $103.85   $103.80  
  Purchase #3 $167.66   6.810%   $179.0776   $179.08   $179.10   $179.10  
  Purchase #4 $232.69   10.212%   $256.4523   $256.45   $256.45   $256.50  
  Purchase #5 $116.69   13.672%   $132.6439   $132.64   $132.65   $132.60  
  Purchase #6 $147.97   9.201%   $161.5847   $161.58   $161.60   $161.60  
  Purchase #7 $66.31   13.369%   $75.175   $75.18   $75.20   $75.20  
  7 purchase totals = $902.71       $986.0387   $986.03   $986.10   $986.10