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 $232.40   13.864%   $264.6199   $264.62   $264.60   $264.60  
  Purchase #2 $194.37   4.676%   $203.4587   $203.46   $203.45   $203.50  
  Purchase #3 $29.69   13.505%   $33.6996   $33.70   $33.70   $33.70  
  Purchase #4 $157.26   3.556%   $162.8522   $162.85   $162.85   $162.90  
  Purchase #5 $110.70   9.169%   $120.8501   $120.85   $120.85   $120.90  
  Purchase #6 $138.48   12.568%   $155.8842   $155.88   $155.90   $155.90  
  Purchase #7 $127.54   11.356%   $142.0234   $142.02   $142.00   $142.00  
  7 purchase totals = $990.44       $1,083.3881   $1,083.38   $1,083.35   $1,083.50