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 $152.96   8.118%   $165.3773   $165.38   $165.40   $165.40  
  Purchase #2 $186.98   9.702%   $205.1208   $205.12   $205.10   $205.10  
  Purchase #3 $23.94   7.392%   $25.7096   $25.71   $25.70   $25.70  
  Purchase #4 $54.57   5.835%   $57.7542   $57.75   $57.75   $57.80  
  Purchase #5 $162.26   11.210%   $180.4493   $180.45   $180.45   $180.40  
  Purchase #6 $201.29   8.771%   $218.9451   $218.95   $218.95   $218.90  
  Purchase #7 $97.26   6.857%   $103.9291   $103.93   $103.95   $103.90  
  7 purchase totals = $879.26       $957.2854   $957.29   $957.30   $957.20