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 $84.32   13.833%   $95.984   $95.98   $96.00   $96.00  
  Purchase #2 $200.95   3.301%   $207.5834   $207.58   $207.60   $207.60  
  Purchase #3 $32.56   5.300%   $34.2857   $34.29   $34.30   $34.30  
  Purchase #4 $31.79   7.600%   $34.206   $34.21   $34.20   $34.20  
  Purchase #5 $182.44   12.131%   $204.5718   $204.57   $204.55   $204.60  
  Purchase #6 $107.78   12.337%   $121.0768   $121.08   $121.10   $121.10  
  Purchase #7 $117.40   4.853%   $123.0974   $123.10   $123.10   $123.10  
  7 purchase totals = $757.24       $820.8051   $820.81   $820.85   $820.90