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 $218.33   12.807%   $246.2915   $246.29   $246.30   $246.30  
  Purchase #2 $83.51   5.552%   $88.1465   $88.15   $88.15   $88.10  
  Purchase #3 $118.35   7.801%   $127.5825   $127.58   $127.60   $127.60  
  Purchase #4 $160.31   10.702%   $177.4664   $177.47   $177.45   $177.50  
  Purchase #5 $57.94   11.324%   $64.5011   $64.50   $64.50   $64.50  
  Purchase #6 $145.32   9.422%   $159.0121   $159.01   $159.00   $159.00  
  Purchase #7 $154.79   8.705%   $168.2645   $168.26   $168.25   $168.30  
  7 purchase totals = $938.55       $1,031.2646   $1,031.26   $1,031.25   $1,031.30