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 $78.92   3.506%   $81.6869   $81.69   $81.70   $81.70  
  Purchase #2 $31.81   3.676%   $32.9793   $32.98   $33.00   $33.00  
  Purchase #3 $211.89   6.445%   $225.5463   $225.55   $225.55   $225.50  
  Purchase #4 $31.49   3.437%   $32.5723   $32.57   $32.55   $32.60  
  Purchase #5 $80.92   7.767%   $87.2051   $87.21   $87.20   $87.20  
  Purchase #6 $161.50   3.408%   $167.0039   $167.00   $167.00   $167.00  
  Purchase #7 $34.60   4.863%   $36.2826   $36.28   $36.30   $36.30  
  7 purchase totals = $631.13       $663.2764   $663.28   $663.30   $663.30