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 $29.40   11.141%   $32.6755   $32.68   $32.70   $32.70  
  Purchase #2 $163.47   11.140%   $181.6806   $181.68   $181.70   $181.70  
  Purchase #3 $35.26   8.185%   $38.146   $38.15   $38.15   $38.10  
  Purchase #4 $68.36   10.646%   $75.6376   $75.64   $75.65   $75.60  
  Purchase #5 $96.65   9.804%   $106.1256   $106.13   $106.15   $106.10  
  Purchase #6 $23.49   5.809%   $24.8545   $24.85   $24.85   $24.90  
  Purchase #7 $8.70   4.340%   $9.0776   $9.08   $9.10   $9.10  
  7 purchase totals = $425.33       $468.1974   $468.21   $468.30   $468.20